That sucks. Got us again. Since we don't have a deck mounted, this may or may not be accurate info, Daniel. The belt that was with the 70 deck that was mounted and working when we got it is 3/8w x 57 1/2"lg. Angle unknown. This belt looks about right, but has no marking what so ever on it. Feels and constructed like a "V" type car fan belt. Remember those? LOL
I would rather think the proper width is 1/2 inch and the length slightly longer as in 58-59", just a guess though.
Sometimes the chart will still list the belt specs. for a while after the belt is NLA, but I had no luck finding it. The blade to blade belt, #M41642 is still available and the specs. are with the price at JDParts. It is 62.100lg x .500w x .31tk x 32 deg. I can't find it in the chart either, must be doing something wrong. Metric, maybe? I'm going to keep looking.
Standard fractional HP belts at the auto supply store might be 30 deg., but will probably work fine. Once you determine a good working size, I would recommend the "green" or "blue" belts that cost a little more, but do last longer in this application.
Good luck, Daniel. I'm gonna go through the same thing with the deck belt for an STX 46. Last time I looked it was $70. Likely higher by now. It will no doubt become NLA soon, too.