Assuming your ProMax is a round reel and has the original gears, they are 5.3:1 You got a steal! I've bought ProMax's on Ebay and they go for 10X what you paid. They are superb reels with a lifetime warranty and Abu Garcia still stocks parts for them. The original cost was $169, in the late 60's-early 70's. Put Rocket Fuel in the spool bearings, install 2 black or 1 white brake block, loosen the cast control until the spool has a tiny bit of sideplay (i.e., all the way off) and it will cast lures or pitch jigs all day with nary an overrun. I have a bunch of new reels but the ProMax still casts better and fishes like a dream. You can change the gears to 6:1. I switch the handles on mine out for handles from a C3/4600. The bearings under the paddles on the ProMax tend to rust and bind. The simpler C3 handles are a good color match and work better, for a $5 investment. BTW, the spool bearings are 3x10x4 mm, same size as a Curado 200.
BTW, the real 'little brother' of a 3600 is the ProMax 1600. Same reel, just 1/2" narrower. I'd call the Black Max 'poor brother' : Casts as well as the ProMax but not quite as smooth with fewer bearings. But its black finish holds up better than the flaky stuff they put on the Promax!