[the-chauffeur]

Why not just change the cylinder liners rather than mixing and matching the whole assembly? Then you've got no worries when it comes to oilways or any other passages.

Stick the barrel assembly from the bike in the oven at around 200deg C for about ten or fifteen minutes and you should find the liners drop out - you sometimes hear a clang as gravity acts on the case and it drops down the liners. Repeat with the donor and while they're hot, switch the liners from one to the other. Place the final assembly face down (so the face that mates with the head gasket is resting on the tray) and heat it to get the liners in place. Again, gravity is your friend but this time it's to get everything seated.

Once everything's cooled down, check for flat on the head gasket face. You may need to flat that face with sandpaper if there's any discrepancies. Search YouTube for flattening an engine block to see how easy it is.

 

[the-chauffeur]

Putting a newer set of cylinders on an older bottom end might not be a problem, but that'll depend on whether the diameter of the holes on the '8' version (which I assume are engine stud holes) that are responsible for carrying the oil to the top end. So long as there's sufficient clearance for oil to be pumped to where it needs to be, go for it.

Chances are Honda used the same bore for all of the studs, so if that checks out - and everything else lines up - you should be OK.