87 318 build question

Yes, you can put a flat tappet cam in a pre-magnum roller motor. As a matter of fact some came from the factory with flat tappet cams. I have a '88 360 that has the provisions for the roller but a flat tappet cam stock. I am going to do the opposite, I purchased a set of roller lifters, pushrods and spider from someone on this site and I am going to replace the flat tappet cam with a roller. The roller cams cost more but you can get by with a bigger cam and still have it streetable. Not to mention that there is less chance of the cam going flat. Comp Cams has a good selection of cams for stock roller motors.