yes header will be a problem and if you use a after market head it dose not help some ex ports are 3/4 hi and things get in the way like the steering shaft you will have to cut it down and use u joints and make a set of headers and make a new alt brakets this is not to bad but it is time and money a good built 396 will out run a stock tall deck . here are some things to think about you need a msd or cut a distributor for a slip collar if you use a stock deck type intake with plates if you use tall deck intake some are cut down for a stock distributor .i can not recommend this for a stock type 427 talldeck .but if you want a big engine this is the type of block you will have to use you can get 526 out of the stock block and some more but the wall will get thin. i could write a book on all the things i had to do to get the tall deck to fit in the gto s I did this so i could put a 572 big block in them and now i have a 630+ in the one i drive on the street this is a lot of work but it can be done .if you want more cubes than a 526 you need tall deck bow tie or world or dart . the donovan is what i use but to put a bigger engine in you need a bigger oil pan and then you have to cut the front cross to get room for pan and you have to move the center link and make new pitman arm and idl arm or put a rack in i had to make my oil pan for my donovan i had to make a lot of stuff so you need a small michine shop and a tig and a mig welder would help