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

300 hp + PG + 2.73?
The amount of cam you'd need means a high-stall converter, which means it will slip at 60 with 2.73 gears.
The L6 needs more speed equipment than an SBC for the same HP per inch. 300 from 250 takes more parts than 420 from a 350.
A compromise: you could get a lot of the effect from doing an excellent job on the head, manifold, carbs, exhaust, ignition, but leave the cam alone until you re-do the block and sort out the chassis to keep the moderate RPM range and low-speed torque.