Just exploring some options.

Mercury sportmaster lowers come in standard -1 and -2 also. Notably Longer skegs and slightly different shaped nose cones.

So they wouldn't perform as well as the Imco's?

That's not necessarily true, every boat is different. A lot of guys run the sport master lowers and a lot run the imco. Seems like a lot of the guys who race boats use the sportmaster lowers (not sure if that's just a coincidence)

BMAX makes a shorty lower. Personally ran them and worked great

Mell Riggs told me that sports master run better on cats and imco better on v hulls My 2cents

are there some general guidelines to prop shaft height on a single i/o application in relation to speed?

i have 595 hp doing 75 mph at 6000 rpm on a less than desireable signature 4-blade prop with my prop shaft 6.25" below the hull when checked with a straight edge.

advice on my setup?