What type of vintage semiconductor device is this? Is it an SCR?
It matches rectifier Case 175-03 or 253-03 used on SCR's with an obsolete P/N made in 1987 week 39 (8739).  Appears to be rated for about 25A with 4 switches to serve as 2 half-bridges for 2 loads with variable phase or ON/OFF control.  It takes 2 SCR's to make a Triac.

Also obsolete from 1987 is the latest cell phone. My friend had one of these.