Inliners International Forums General Discussion Engines Deciding what to do to my 250

I'll let others speak to the multi-carb route.
Yes to heating the intake.
Yes to HEI.
Other cams to look at - Schnieder Cams in CA.
Stock head limitations? You hit it on the head (pun intended)
Lumps in the intakes, larger valves, with mild blending is the simple and cost effective answer. Lots of info and several vendors of lumps on this board.