Part 1: Stihl 064 to 066BB Conversion- Drilling and Tapping Crankcase

This video explains a bit about installing an aftermarket Stihl 066 Big Bore top end made from Bailey's, onto a 064 bottom end. This is Part 1 and it covers drilling and tapping the crankcase to fit the M6 x 25 spline screws that are OEM for an 066.
I could not find any video tutorials explaining this somewhat common upgrade for the less expensive Stihl 064 (85cc) conversion to a 066 BB ( 99cc).
The video is pretty long, and it's meant to be because I have some informative commentary along the way and I want to show the entire process highlighting potential hiccups you may encounter etc.

[@Houseworksaws]

Actually this is very very handy info for people doing this swap. I’m doing a ms650 with a oem 064 top end so I need to slot my holes in the cylinder to make it able to bolt on.

[@harryrambo4564]

Much easier to just oval the holes on the cylinder, thats what I did when I built my 064/066

[@davidnisbet2057]

What's the deal with it do they just not line up right? You oval all 4 holes or just 2?

[@alexstromberg7696]

Do you just drill them up to m6? Nothing else and it fits?

[@materman951]

Did you finish this build? How did it turn out?

[@KSInCalifornia]

Yep, I've done it to two saws now. She rips