This is new-old stock. All I know about it is that it was included in a ham radio QRP kit as a generic "medium power RF transistor." It is also probably quite old. The "712" numerals could be the Julian date code of 1971-2.
I've Googled this thoroughly but come up with nothing. Anyone know how to extract a base part number from the markings?
It's from Motorola and probably circa 1971 as you say. At the time they used MJ, MJE and MRF as prefixes but I can't see any match on those numbers, possibly it's a house code rather than part number.
From the package I would suggest it is similar to the BD131 from Philips which was commonly used as a low power RF amp up to about 1W/30MHz.