I have a carb on a 305 ho vortec engine in one of my cars that runs ok, but for the most part, it's not a good idea. Here's why, the ecm is constantly making air fuel and timing adjustments and the cam is designed to operate in those peramiters. It's virtually impossible to imitate this with vacuum advance, etc. Depending on your desired performance, it may be more trouble tuning it than it's worth. With that being said, one could assemble as is and plan on a cam swap as a update later in the life of the build. I do know of several examples that went wrong, poor performance, mainly timing related, preignition, etc... do some research before investing in any parts, imho. As for going from roller to flat tappet, I don't know from experience, but flat tappet cams are held in place by the force and friction of the lifters and the lifter bores are designed with this in mind in engines designed for flat tappet cams. Roller cams are not this way. I would be apprehensive to try it. I know roller cams are pricey, but the lifters should be able to be reused and that's half the cost. Roller is better and your springs are also designed for it. Again, do your research with a cam manufacturer to save some potential aggregation. I know of one specific example where the builder didn't want to spend any money on the valve train and just wanted a smooth running cruiser, so he bought a good running stock fuel injected engine, spent a fist full on an intake, carb, and distributor, but ended up with a timing computer and a hefty investment of time and cash to get it to run right. The issue was timing. That was a 360 Mopar, but the same sort of issues may come up.
