Oops, forgot about the smaller register of the early 273's. One interesting factoid: When I swapped a later 225 into my 65 Valiant, I had to open up the pilot hole in the flywheel to fit over the later crank. But when I swapped a 340 into my 65 Barracuda, the 273 flywheel fit perfectly as is. I haven't had a 273 crank to eyeball in almost fifty years, but I assume from the foregoing that the early 273 crank register has the same outside diameter as the later ones, but a smaller inside diameter?? So it could be machined to clear a later torque converter?
Anyway, as to balance, according the Hot Rod's December 63 article about the new 273, since the 273 crank and rods were the same as the 318, but the pistons were lighter, "an extremely heavy-walled piston pin is used in the 273 to bring total reciprocating weight up to that of the 318. This eliminates the need for special balancing. . . ."
