Back when my dad and uncles had 3 GT dryers they had quite a hodge podge of tractors that got used on them.

2-65 White (Iseki) diesel ran them good
1655 Oliver diesel ran them good
720 JD diesel ran them good
730 JD gas ran them good till it burned up

2-105 White and 1855 Oliver would both run them on the 1000 pto at half throttle

630 JD gas didn't have quite enough power so the line for enough power is somewhere between a 630 and 730 


Like the other guy said you don't have to unload full speed or you could park a wagon under it to use as a surge bin.    We always wanted to get them empty and full again as fast as possible.