B & M Hydro Tags ?

I have two B&M Hydros and I need help decoding the ID tags......................
One reads O 53 - D5 U 3973
(flat pan)
.... brazed chevy torus
..... I thinkk it stands for '53 Olds unit
........ h 7 maybe 88 tailshaft ?
........U (unblown or ??
......3973 might be production number ?

Second one reads P 55 - H7 UC 519___
(slant pan)
..........brazed chevy torus
..........think it is a '53 Pontiac
..........H 7 ? maybe 98 tailshaft ?
......... UC ? no idea oe unblown comp.?
............519__ __ ? production number

Thanks for any help

 

Both seem to have the smooth top regulator spring cap. And even though one is a D5 and the other a H7, they both have the short tail shaft(I think they are 88's ?)

But it is the U and the UC I can't figure out

 

I remember when the first unit was bought new, it was for an unblown street '62 Corvette, but later he ran it blown. And it has some cut fins in the torus.

the second, Pontiac unit, has the OEM Pontiac bellhousing plus a B &M adapter that mates it to ,what I think , is a 421 Pontiac motor, but no flywheel that fits the small Chevy type torus. I have read before that all out comp B&M's used the smaller torus in order to get more RPM's out of OLDS, Pontiac and Hemi Morors but never understood how they ever mated rhe larger Torus covers(flywheels) to the smaller shells? I have a Pontiac cover and see no way to make it work?

 

OK..........I think I got it ! but,,,,,,,,,,,,you can run the smaller toruses (driving and driven) inside of the 30 bolt covers ?