any thing that bolts to the head like the ac and alt and has any thing bolted to the intake will be to short if you use stock low deck brackets. if you use a alum head they may have a rased port may be abit harder to over come this with short deck headders . and there other things you will have to deal with you can get 512 cid out of a 454 stock block and about 530 out of a tall deck the work need to make the tall deck work it may not be worth it less you can fab all the parts and make headders or very deep poctets i have a 632 under a stock gto hood so yes you could get the hood down but i did alot of work to get the engine down in the frame made engine mounts. cut the crossmenber and box it . lower the cross link and build a new pittman arm and idle arm . cut down the steering column to help with more room for back tube and run steering joints cut the steering shaft for bouble D shaft