Houston we have a problem. The roller lifters are longer than standard flat tappets. So my understanding is that when you use them in an early block with a standard base circle roller cam it pushes them up too high - they interfere with the dog bones. So, you either need to use a smaller base circle cam (which lowers the lifters - the block will have to be drilled in the lifter valley so the spider which holds down the dog bones can be installed), or go with a set of aftermarket linked lifters (expensive). And after you go through all that, you'll likely need custom length pushrods as well. The cam you pick will determine the firing order. If you intend to use efi - you need to match the computer you're using to the cam in terms of firing order. So, a computer out of an HO (Mustang, Lincoln) will be needed to use an HO-based firing order cam. Clear as mud? You'll have to talk to the cam companies about HO firing order cams in a flat tappet grind. Be VERY specific about the firing order you want and the fact that it's not a roller, if you end up going that route.