chengine differences

Hi Again Guys;
Did a second build for the auto parts guy down the road today.
Build went sweet.
I do have questions though...all 66/80 engines not alike?
Appears not. The transfer slots on the side of the cylinder between my engine and his had a different configuration. Mine has rectangle or squared off
look to it while his has a somewhat triangle look. just on the outside. What gives? His also ran gobs better than mine staight out of the box. I am still trying to get the 4 stroking out of it. Mine has the "epa" muffler or catalyst and his does not.
Any suggestions or comments welcome.

Thanks
Bobby

Hey thanks for the info and feedback.
So it would seem chinese quality control and military intelligence are under the same classification..............oxymoron
lol
Bobby