I have a 460/c6 in my 67 stang.No spring tower mods needed.I used homemade engine mounts and moved the engine back as far as it would go.Also moved the raditor support forward 2".I suggest a header kit from speedway and the c6 trany.Plenty of room for a turbo & more room if you dont have ac/ps.
Back in 68 I worked for a big ford dealer on long island.We allways had the factory reps visit with parts like that.One time they did bring several of those cross boss manifolds & inline carb setups.I still remember some of them did not have a idle circut.They were made for racing engines that...
I allso have the 351w in my 67 fastback.I refused to spend the big moneys for the headers. I went with the 289 stock cast iron exhaust manifolds & then added a stainless 2 &1/4" exhaust system.I didn't have to clearance the z bar or steering box or idler arm or shock towers.
