I installed a set of gears from a 1961 8 3/4 into a 1968 housing. Before installing the gears, I noticed that instead of a round shaft between the spiders, for the axles to butt up to, there is a large square shaft. I didn't think much of it, but now that the axles are back in, I have a bit too much end play on the left axle.
I adjusted the right axle as usual, thumping it to seat, backing off a few notches, etc and the right axle is set perfect. However the left axle has quite a bit of end play. Makes me think that the the big square block in the 1961 gears must not move at all, and isn't transferring the load across to the left axle. This would make sense I suppose since in 1961 the axles relied on shims for end play on both sides.
So now what should I do?
I suppose I could use a right axle on the left so that I have an end play adjuster.
Anyone encounter this before?

I am well experienced in 8 3/4's and am very familiar with their setup