It's 30 years since I worked on L2's so to refresh my memory, I had to wander down to the local AGCO dealer to check on the thresher set up on an old wrecked L2 they had way down the back of the yard.
Yes, you could make the thresher / concave clearance adjustable while on the go from the cab and the conversion is not very difficult.
In fact it is probably quite simple.
It would just be time consuming and cost lots of $$$$$$!
Note that the thresher bearing support plates are pivoted at the rear and the concave clearance adjustment threaded rods are anchored near the bearing housing on the bearing support plates with another anchoring stud in the slot ahead of and in front of the bearing.
All of these are locked down tight to prevent any unwanted movement in the thresher settings.
The adjusting rod nuts lock the bearing plates as any movement of the thresher under the shock loads as it feeds plus any out of balance forces in the thresher itself will rapidly wear all the components on those bearing plates and the adjustment rods if they are at all loose in any way.
However if a close check is kept out for wear in the plate components when a cab operated thresher clearance adjustment system is fitted then you might get away with the following but don't take my word for it.
1 / New thresher bearing plates made from at least 6 mm plate.
2 / Adjustment rod anchor points to be moved as far forward as possible on the bearing plates to give maximum leverage and maximum adjustment movement in the new adjustment system.
3/ Two very heavy duty linear actuators, each on it's own electrical circuit using relays in the circuitry as the power consumption on these heavy duty actuators can be very high while they are operating.
These linear actuators are fitted so as to take the place of the threaded rods to adjust the thresher clearances and settings.
Examples of possibly suitable actuators which will possibly be capable of taking the shock loadings from the thresher are following.
http://warnernet.com/litportal/pdfs/P-1581-WL pgs 10-33.pdf
With this last make, Linak, [ 2500 newtons is equal to about 560 lbs force. ]
These linear actuators of which there are many makes, would need to be capable of at least 500 lbs each loading and I would go for a thousand pounds if it cost very little more, not to shift the easy load but to handle the shock loads which will be transmitted in full to each of them as you will not be able to lock any slots or pivots points down if you use this system.
As you can see from the illustrations, linear actuators can be made quite compact, particularly if their required travel distance is also very short.
The linear actuators would only need some 4" travel depending on the bearing plate anchor points.
The slack or movement in their internal nut / threaded ram system of the actuators would have to be minimal to prevent rapid wear as the thresher pounds away as the feed varies to the thresher.
Any internal movement in the actuator adjustment nut / rod will lead to rapid wear.
Most important to get the travel speed of the linear actuators right down to perhaps no more than 100 mms
[ 4 "] minute otherwise you will constantly overshoot when trying to adjust.
Generally very slow actuators are also very heavily geared and can handle high loadings, all of which is needed here.
Talk to any suppliers or better to the actual manufacturers or the main distributors as any retail outlets will probably know stuff all about linear actuators.
No two actuators will move at exactly the same speed so separate electrical circuits are needed so that each actuator can be adjusted individually.
You are aware of the belt adjustments needed .
Also there will be a need for a thresher clearance scale for each side of the thresher which will possibly need a somewhat magnified or increased amount of movement relative to the actual thresher adjustment to be able to read the amount of adjustment with some accuracy.
To take this a step further;
Here in SE Australia we always had a lot of problems with walking grain over in cereals as for some reason our climate and our soils grew a straw that broke up, formed a mat on the walkers and over went the grain.
And believe me, we tried every thing we knew to try and fix that problem but nobody really got fully on top of it until the rotaries came along.
One thing I did to our L2's which increased capacity by about 15% and reduced walker loss substantially in cereals was to cut out the flat section of plate which is a part of the concave frame, just behind the actual concave proper.
this part of the concave is also under the beater at the rear of the thresher.
I installed a cell grate in this area [ from memory ? width across thresher by about a foot or so fore and aft ] using 3mm x 25 mm steel strips on edge at about 25 mm spacings.
I made filler bars to fit the cell grate so that if it did not work we could just install the filler bars [ by crawling in through that hole on the LH side. I was 30 odd kilograms lighter and some 35 years younger in those long gone days!
] and go on as per usual.
We ran the L2 for about an hour or so with just the cell grate and then installed the filler bars for a check.
They lasted about an hour before yours truly was back inside of that L2 pulling those filler bars out.
They were consigned to the "reuse sometime on something else shelf" and never used again in the L2.
The beater knocked more material, particularly grain down through the cell grate onto the raddle from where it went to the sieves instead of the walkers.
More material on the sieves but as we never had a sieve problem with the L2's this was no problem.
Good luck if you decide to do anything on that thresher adjustment.