2388 unloader tube length for 35' head?

The discharge from the 208" auger is about 21 feet from the centerline of the combine. A centered 35' draper is about 18' from the center line of the combine. So you've only got about 3 feet to clear the truck with the side of the head and still get the grain in the truck. Probably not enough unless you like close shaves.
Now if it's an offset head, that gains you 2-3 feet, which is probably enough.

Thanks for the info, sounds like I'll need to extend the auger or get a different boot for the end of the tube, anybody have any recomendations on types to use?

Maurer makes a aftermarket extension for your combine. I think they said it will add 3 feet to your auger. Here is the link......... http://www.maurermfg.com/theextender.html

We put a 35' 2020 on our 2388 last year. Was very tight unloading into semi's. We put a stewart steel extender on and it works well, We even unload on the go. I think it added about 2.5 feet and was fairly simple to put on and the boot design shoot the grain out a little further. Only complaint is it seems to let more grain leak out after putting the auger back in than the stock auger. I believe its the same one that maurer mfg sells.

How well did it handle the 35'?

We had to add the 3rd lift cylinder. I can't remember if we loaded the rear tires or not. I don't think we did. But we did install a mud hog in the rear. We had to mess around with the angle alot to get a good cut, won't cut as tight as the 25' 1020. Our 2388 does not have duals. I think that would make it handle alot better. We will probably add duals the spring. seem to have more trouble with beans plugging the front of the feeder when they are getting tough. It puts alot of stress on the feeder nose hear alot poping and cracking in the feeder, nothing broken yet

I just got the head, put in the adapter plate and tried to lift it with just 2 cylinders on the feeder, it wouldn't so about 45 mins later we had the 3rd cylinder installed and it lifted it no problem, I'm not sure how much weight the frames of the 2300 series combines are rated for but I have bin extentions and now a 7000 lb header, any trouble with any frame cracks? or ideas on what to beef up before a poss. failure somewhere do to the extra weight?