Can a 273 crank be balanced to 340 specs ?

Today's pistons can be quite a bit lighter than the stock 273 or 318 pistons, you can also get lighter pins and rings
so all is not lost
with careful parts selection you might even duplicate your OEM balance and not have to balance :)
Weigh your old parts and do the math
but also what YR just said after I wrote the above
I do know when we were racing 340s they did lots to get the rotating weight down