Just do it, I can see no problems. The cam lift is indeed in the ballpark. 340 springs should not be in coil bind with that lift. Retainer-to-guide clearance needs to be checked and possibly modified with a flat file, but I doubt it will need to be done. The solid cam will act like a slightly smaller hydraulic cam and with your compression you will not be overcamming the motor. I don't think it will need a high stall converter, but the 318 will have a lower stall speed than a larger engine with the same converter.

I think your mileage would be within 2 mpg with the new cam but same converter.

R.