depends on what your doing.... If your using the 400 short rod the engine could really benefit from a larger runner head..(180-195) well so clould the larger 350 rod...more so the short rod....

A shorter rod means faster piston speed which in turn needs/uses more air.....

That why the 400's suffered so much they needed way more head than they had....

A shorter rod moves the piston away from TDC faster than a longer rod....

All in all I would opt for a nice 180 cc runner head In cast iron....