I don't know about the rockers and pushrods, but I would be very careful about changing the balancer without tearing down the short block first. I was recently considering a 413 M/H engine myself and got an education from a friend. Many of the M/H and industrial engines had very heavy 4 ring pistons in addition to the LY rods. If there is no "ring ridge", and you have a ring compressor, then at least pull out one piston to see.
If they are the heavy pistons, then you can replace with lighter "car" units and a rebalance will only require removing weight. I'd bet you can bring the rotating assembly to neutral balance, increasing your balancer and flywheel options.
Also, I'm betting you'll need to change the oil pan.
Mike in FL