The significant factor with Healey oil pumps is the type of pump: rotary or gear. Earlier cars came with the rotary type which, in theory, can deliver greater flow (conceivably, greater pressure). Later on, BMC started using a gear-type, with gears made of sintered iron (basically, pressed metal filings). The rotary type can move more oil at low RPM, but it was found the increased pressure on the cam gear could cause premature wear at higher RPMs, so BMC started using gear-type in the later 6-cyl cars. I don't know exactly when or on what models this change occurred; I also suspect the gear-type was, er, more 'economical.' IIRC, an 'extra' tooth was added to the shaft gear to reduce the load as well. Manufacturers, at least AH Spares and DWM, do point out the different applications.
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Low indicated pressure at hot idle is common; first thing to do is check your gauge; when I had my safety gauge rebuilt and calibrated I 'found' another 15PSI of oil pressure at hot idle (OP should never read above about 60PSI, that would indicate a defective relief valve). Also, check for a worn rocker shaft and/or bushings, that can cost a few PSI. I bought a DWM rotary-type when I last rebuilt my BJ8's engine, expecting at least a small increase at hot idle, but got none; on inspection, I found out the previous pump I'd installed was rotary--back then, I don't think the sellers distinguished; they sold what they had on the shelf.
I'm sure Doug or Richard can add to this, or correct my recall of events.