Some money is saved on an L6, they need only 75% as much:
valves
rod rebuild
seat cutting
cylinder boring
tappets
rockers
pushrods
valve springs
rod bearings
But:
7 mains instead of 5
But the piston price is based on sales volume, so the cheapest piston will be SBC 350.
Head/block milling may be more $$ because the surface is larger.
IMHO regardless of use, higher compression (up to the knock level) adds vacuum, torque, power, and mileage, but in a 292 requires a non-OEM dome shape and close P-H clearance.
If a flat & zero deck dome is below 9:1, you need a dome that's specifically shaped for the 292 chamber. This resembles the Chevy V8, but not close enough for my taste. Some piston mfg. have this shape (even if they don't advertise), do you know how close the 292 chamber is to the 250 (which they may have)? Are you comfortable with a die grinder???
