Hi,
you may need to seek out a company that reconditions turbo's. At the Dealer we used a local company that did specialized work including turbo overhaul--we got hot end shaft seal ring grooves built up and re-machined, center housing bearing and seal ring bores re-sleeved and so it went on.
They may be able to set you up with a later replacement turbo with little modification needed --the turbo charge pressure is a fairly low pressure on these old girls from new likely around the low 20" of mercury pressure--10 to12 psi. I stand to be corrected as my old Rack Setting Book only has the 922A specs.
Hope this helps.
Cheers,
Eddie B.