To take the suspension explanation a step further - the Gremlin/Hornet/Spirit/Concord front chassis is a front steer unit, with a loaded upper control arm, and a single pivot lower with a strut rod that is behind the lower arm. The strut rod brackets locate the rods several inches inside the frame rails, which limit header clearance, as does the steering shaft. I actually re-located the strut rod brackets to under the frame rails and use heim joints instead of bushings to locate the rear of the rods. As to engine (SBM) location - I used a stock trans crossmember, used a stock V8 904 trans mount to set the trans location, then fabbed the engine mounts to the frame, using A-Body plate style mounts. A stock 6qt. 360 truck oil pan just clears the factory engine crossmember. Headers are modified A-Body mystery brand 1 5/8" that are tight to the steering shaft and the shock/spring towers. I'd say a big block would be very tight, with tower mods likely. Actually, I need to make new headers, and when I do, I will probably ditch the factory front suspension and install a Heidts Mustang II kit, or possibly one of these Welder Series kits.

http://www.welderseries.com/blog/#!/Front/c/12959481/offset=0&sort=normal

Another option I'm considering is installing 90ish Fox body struts with the coil-over kits and upper caster/camber plates and trimming the towers back.