This isn't HPF. HPF is the same size as an F40/RS HPF. If you unbolt it the date is stamped on the back. It should be something like B 89 or something (Feb. 1989)

Okay. It's NPF for sure them...was there ever a green/yellow label version of this like the 446 ones?

I think the green/yellow label was only for the HPS ballasts. I have and 80s single lamp NPF Universal that's a light blue and yellow label. are the corners on this rounded or angled? if round, this ballast might be a late 70s ballast since i have a trigger start ballast like this.

Squared off and you mean HPF right?

yeah I meant HPF not HPS lol. BTW, i was referring to the corners above and below the labels (the tops of the long side of the ballast) . the rounded ones are older.

Still squared off...what's with the "For Use in a Portable Lamp"?

I think that means is is for a fixture that is a cord and plug connected and not hardwired into the buildings electrical system

Maybe it means that it's suitable for use in portable fixtures? Still vague though.

Right now this has a 2-prong cord wired to it like most of my fixtures do!

Watch out for ground faults.

I have checked for that BTW can F96T12 slimlines have issues starting if not grounded? Mine likes to light only one lamp (Doesn't even matter which it seems) but touching helps it seems! (It's wired to a 2-prong cord and suspended, like most of my lights are). The lamps are pretty healthy....they're 1996 Sylvania 60w cool white Supersavers.
BTW this above ballast starts fine ungrounded and without the reflector whereas another single lamp one I have hates starting without the reflector! It seems lamps with cathode guards (namely Philips) are more "stubborn" I guess. Anybody have any other theories why?