I would look for a good local shop, really I think the best bet if it is broken parts would be to secure a replacement. I am unsure about the availability of the older transmission parts. There is a robust parts network and rebuilders for everything SM420 and newer because the off-road guys use them to. You could try giving Novak a call for ideas, they are located in Logan, Utah and I have sold them a ton of cores, Google them.
