273 dilemma
if the rest of the motor is in good nick, i'd scoop up a used crank (318 or 273) and go that route over dropping the coin for a 340.
snapping up a cast 318/273 crank local with a trip to the balancer (just in case) would probably be quite a bit cheaper than a 340 crank or getting something shipped, or going motor swap.
keep the 273, that's what makes the car unique.