It has to be said, especially from my position as a lardy 6 footer, that thumpers don't lend themselves to chop building, the engines either look lost in a huge frame or the bikes end up like scale models of a bobber or chop.
I'd say that there are only a few thumper motors that convincingly do the job:
Panther
DR800
SR500 (but even that is a tad small)
Er... can't think of any others.
Most Japanese motors developed from off-roaders have very short crankcases which don't look the part.
Would you agree with that or have I missed the point?
GC