The older T150 and subsequent T170 rear axles used the same vacuum shift housing assembly, I have actually changed between them. Since the later T170 could be had with electric two speed shift, and it was not an uncommon swap back in the day to go from vacuum to electric.. I'd say your probable T150 axle could be made electric, you'd just have to find a later electric shift motor/housing and associated switch gear.
The bigger issue is finding parts for that T150. It's a great old axle, til it needs bearings and the larger diameter (IIRC from back in the '90s when I did this dance with my own bus) differential side bearing race has to be fabricated, because they do not exist. It's also pretty much impossible to find a taller ring and pinion for it.
I like the idea of the two speed rear axle, I think it's more versatile than merely an overdrive, while being a whole lot easier to use than a Brownie. It is even possible to buy a brand new two speed Eaton rear axle of approximately 17,000lb capacity. Then you would have an axle that would last til the sun burns out and if not, you could get parts for it.
When I switched out the old T150 axle under this bus for the newer T170, you could still get parts for said T170 at the dealer-it was the modern option. Now, 30 years later.. it isn't.
