Motor size

49cc has 6mm head studs and the 67cc has 8mm head studs, once you see a few you will see the difference in cylinder size and by the way the cooling fins look as well as the ports on the side of the cylinder wall

I saw a picture last summer of three sizes of 2 cycle motors lined up, and each was progressively wider throughout.

But I got a slant head 50cc a couple months back, partly thinking I'd have more crank clearance on a 10 speed build-

and it turned out that the base of this motor is exactly now just as wide as my 66. So I'm wondering if they may be only changing the cylynder head portion these days.

Luckily I was already covered with a long crank axle from Sick bikes.

The 50 slant has also eliminiated entirely the carb intake, securing the carb right on the motor with long bolts they are calling "steel sleeves" Now I'm just two cables installion away from finishing the build and trying it out. Just haven't had the time or energy.

Judging from the way the performance of the 66 improved with the short billet intake- I think this intake-less arrangement might be good.

Heres the new motor- sorta wish I hadn't painted it now.
and the new billet on the old motor- fantastic! I highly recommend for the small investment.