Can a rotating assembly using a non-counterweighted crankshaft be balanced?

As long as the rods and pistons are light enough, almost anything can be balanced. But eventually you have to put some weight somwhere in most. The 292 six in Leo's car (turbo, methanol injected) has a factory crank, counterweights cut drastically down and shaped is balanced internally. 6 cylinders have an inherrant out of balance around 6300 if Leo is correct. But this one holds up fine at around 650hp. The early Model As and Dodge bros stuff was not balanced and the 4cylinders have an opposed throw close by. They were never expected to rev very high (think like an old deisel). Run lightweight pistons and aluminum rods and you dont need much weight to balance them.