Rob:

I'm not sure of which models interchange on the four stroke OS engines, but I'm sure a little research will tell you which model Magnum engine has the same parts, and they are bound to be less expensive than with the OS name on the boxes. Possibly Hobby People knows the parts you need.

Changing the cam, be sure to replace the tappets as well. And replacement valve springs are also recommended. Should be no worry with the carb. Even if you have to get the cam and tappets from Tower, the Magnum carb from Hobby People should be a bolt-up.

If you find all the parts have to come from Tower, check the price for a new Magnum complete after you get the part prices from Tower. The new Maggie might be the better deal.

Bill.