can not put the bigger carb on with out an adapter and you will not gain if not lose driveability .you will have to change cylinders a good choice anyway. as for head the is a little differance between years and sleds but not enough to search for,the main thing is the direction the sparkplug points older seems to lean towards the carb side the new sleds towards the exhaust side
246 is the same chassis as sm/gp 292. the sl engine is the small carb now rember the reed valve enging also used small carb mount (these have a 4 boult square plate with reeds betwwen carb and motor:gp292 "F")
I just picked up a gp246 197? for $50..couldnt go wrong with that. From what i have found the first year that the 246 came out was in 1974. The carb does not have the 4 bolts to the reeds, only 2 bolts and what looks like a normal spacer.
Did they make the gp246 before 1974 without reeds??