Good morning, Cliffy;
Not all of my ROKKOR lenses sport genuine original Minolta labels on their lens caps. In fact, for the front of the lens I prefer the Tamron brand squeeze lens caps. The 55mm size is the Tamron Snap-On Lens Cap Model C1FB. The plastic parts your fingers work are much larger and easier to operate. (I admit that I do have big hands; I am 6 feet 3 inches tall.) The common plastic caps that bayonet mount onto the back of the lenses are quite readily available from your local camera stockists. For a lens you are using on a working camera body (not one that sits in a display cabinet), this is a guite reasonable and functional arrangement.
When you get the test roll back, you may be impressed with how well the smaller ROKKOR lenses will perform. Yes, many people like the f:1.4 and the f:1.2 lenses, but for pure optical performance, the f:1.7, f:1.8, and f:2.0 lenses do very well. I use the f:1.4 lenses mainly for the slightly brighter viewing screen that helps me in focusing. I can negate the optical advantage of the smaller lenses quite easily with focusing errors. Something about an excessive accumulation of years.
The ROKKOR 50mm f:1.7 with your SR-T 101b will make a fine combination for you. Keep in mind that by now, they may need a CLA. They are probably 40 years old now.