I've put a 429 in my 1970 mustang and I have a set of headers from crites restoration that I bought used. I was wondering how much horse power difference there would be between the headers and the stock manifolds? I am leaning towards using the stock manifolds. The headers are a nightmare to get in and once their in they prevent being able to work on the steering arms, due to them going underneath everything. Also, I am planning on putting on an electric fan, is there a particular model or brand that someone would recommend? Should it be a pusher or puller. I do have an AC condensor so I was thinking a puller? Thanks for the help.