Sorry to disappoint, I don't have any info on those castings. Regarding the bottom brass nut it would be interesting if comparison could be made between those two. Just to see if the valve without nut has less restricted opening vs valve with nut.
I can confirm that the valve with nut is type 3 for 4 doors cars (the one installed on my car) whereas the valve without nut is type 2 for 5 doors cars.
This from blue Volvo pocketbook..

Without brass nut (the number 2 is stamped on the raised casting - for 5 doors cars):
https://www.ebay.com/itm/ATE-320120-Rear-Brake-Power-Regulator-Valve-for-VOLVO-740-850-940-960-1983-1998/123663926094?epid=7029732122&hash=item1ccaf1c34e:g:nnEAAOSwJzpcdADQ
With brass nut (type 3 for 4 doors cars - part #3546634):
https://www.ebay.com/itm/Volvo-740-850-940-960-S90-Brake-Hydraulic-Line-Junction-Ate-3546634-NEW-B9/202766646206?epid=1739688949&hash=item2f35d57bbe:g:7jYAAOSwesRdZv0x
Amarin.
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