A (forged) 340 Crank is Not a (forged) 273/318 Crank?

Another difference between 273 forged steel cranks and 340 forged steel cranks is the 273 has a smaller centering recess for the torque converter hub (67 and earlier at least). If you put a 273 crank in a 68 and newer 340 or 318 then you won’t be able to get your torque converter to bolt up. The recess can be machined I believe though to accept the larger hub on the newer torque converter.