Attention slant 6 racer's ????

Hemi head will require a crossflow, and a crossflow is going to require a fenderwell exit header as your going to need room around the dizzy and oil pump area.

Chry I caught your saying a 400inch slant, I have to call BS as even with a 4.5" stroke (.375 bigger than stock) and a insane sleeved block for a chevy 305 piston (3.710 if I recall) you come up with almost 300ci, no more bore will fit as the sleeves are already siamesed and maybe a little more stroke could be added depending on rod big end.

anyway if he plans on trying to sell them he needs to just make a stock head out of aluminum, with the potential for a "max wedge" port, catch my drift? this way a mild slant would benefit with off the shelf parts, but up to a full port monster could be fed. also he is going to need to get a good block and have it CNC blue printed to correct bore angle and centerlines, from there he can cheat the valves around to get the biggest valves (~1.8/~1.5) and make it to notch for the exhaust, that should make the greatest clearance for the intake and have room between the seats.

next I would go a really thick deck BUT a closed kidney shaped chamber. I would probably for a 49cc stock deck (roughly 9.1:1 for long rod motor) and 8.75 stock 225 rod motor)

playing with valve angle would be cool but finding a off the shelf rocker gear might be hard, that valve would be getting farther away meaning you would have to move the shaft centerline and have more clearance issues on the lifter valley area OR find a very long tip rocker and go from there.

only other thing would be to get rid of the drool tubes BUT still have lifter access and use the early 13/16 plugs. stock flange rail for int/exh and valve cover.

may think of more