The earlier casting number is more likely to be HR. I think there was two though, one for manual and the other for Powerglide and that one had a lockdown bracket maybe. Dr Terry will know more than me though.

I probably have a half dozen or more hanging in the shed, never really looked to see what they are. All HK GTS’s I bought I wrecked for donor parts for V8 GTS or GTS327 and either threw away or sold any 6cyl bits other than the odd piece kept for shed ornaments, so a few of these intakes will be off those cars. Others will just be $5 or $10 swap meet bits, only picked up if cheap and not corroded. If you wait until Dr Terry sees this thread he should be able to set you straight.