Assuming you have the 18" rear standard Comstar that I think I see in one of your photos, the best match will be the 19" standard Comstar from the '78 Goldwing. It also has dual disc brakes. If you want 18", look at a CM400. Note that the GL1000 front is the same width (2.15") as your CX500 rear, which is a little odd, but at least it isn't wider. If you mount a narrower tire, it should be fine.
Looking up the 1978 GL1000 front wheel bearings in a parts fiche, we see that they are a 6302UU.
Googling "bearing 6302" shows us that is a 15x42x13mm bearing.
Googling "bearing 20x42x13" (to account for your 20mm axle) we find that a 6004-26 or 10BM10 deep grove ball bearing is 20x42x13.4, which will fit both your CBR600 axle and GL1000 hub.
You'll need to work out the axle and caliper spacers.
Randall