Replacing 18.5 Intek with new 21 Intel.mounting holes on new motor are not threaded, is there a reason.

I would say 1) they forgot to thread the holes, 2) it allow threading for whatever thread you choose? or 3, throughbolting?

I would say 1) they forgot to thread the holes, 2) it allow threading for whatever thread you choose?, or 3, throughbolting?those were my thoughts,thanks for the second opinion. I will probably tap them to use the original bolts

Hi,
No they are not threaded. The bolts are made to cut their own. If you look at the bolts from end-on, you should notice that they are slightly triangular and tapered at the end that starts them. Ah the miracles of high-speed manufacture.
An air impact tool will zap them right in, or you can tap them yourself which will allow you the thread the bolts with your fingers.
Peace,
Clarke