I ran a mostly stock 427 high deck with a old school Weind tunnel ram and dual 425 impco mixers on my k20 bogger it was solid combo . Lots of tourqe but pretty much done by 5000 rpm .
Not sure if its in your budget , but propane loves compression , Mill the head , run a thin head gasket, and put some pistons with a little dome in there and it will really wake them up . That and cam and valvesprings were all that I did to that motor
Mine was a well pump engine that I took as partial payment for converting him over to to electric , so the pistons and heads were already done all I did was add the cam and valve springs
