66cc slant head on a 61cc?

I am new to all of this but I am interested if the slant heads for the 66cc engines will fit on my 61cc engine. I am happy with what i have but just cant leave well enough alone! Not to mention my sons slant head engine kit will be here today!

I have also noticed that when looking at the the head to the cylinder i can see day light on the other side near the outside edges of the head! The engine seems to be running fine though. I imagine if there was a head leak it wouldnt run all that well. I got some wet sand paper so I will take the head off and sand it flat on a piece of glass. Figure couldnt hurt. I also got some ultra cooper rtv to help when reinstalling. I dont want to take the engine out of the bike to flaten the cylinder so I will see what happens.

I just got the engine kit today for my sons bike- 49cc from BGF slant head. I had to reverse the head so the plug faces forward to fit in the frame (very tight fit on this bike) and while the head was off I measured the bore and its the same as my suppossed 61cc. Do these engines all have the same bore, just different strokes for the added displacement? My 61(61cc is what the sticker says) does have 6mm studs but no problem for me to drill and tap assuming the casings will allow it. I'm just messing around though, having fun. I am curious on the bore and stroke though of these little 2 strokers.

I will measure the actual stroke between the two engines i have. I am just so curious to see if the slant head will be a better preformer. I suppose i could also go and borrow a compression gauge and really see what is going on in there. Just love my new hobby and all the information on this site!