Major reasons why not make an aftermarket cross flow head for a siamese design?
Needs:
1. new intake manifold (handicap the design to continue use of original siamese exhaust positions)
2. new exhaust manifold (continue original siamese intake positions)
3. needs both
Successful new head requires:
1. Uses existing bolt locations (perhaps with longer bolts)
2. Rockers? Maybe, depends on the chamber shape etc.
3. Oil supply & drain
4. Water circulation
5. Cam - this is a very big $$$ deal. You can't use the original cam (or any regrinds etc.) unless the lobe positions match the new head. For stovebolt and Gen-3 (250, 292):
E I I E E I I E E I I E
Normally, 2 exhaust valve are never adjacent due to temperature problems.
By comparison, a slant 6 is:
E I E I E I I E I E I E
