Yes yours looks to me like late 70s cymbal in terms of lathing, visible hammering, and trademark stamp. The hollow ink Zildjian logo on the bottom was in use from 1978 to late 1982.
Weights for different models for this production era based on cymbals which still have model ink on them are:
Light Ride 2130g (1 example)
Crash Ride 2054g - 2114g (3 examples)
Medium Ride 2400g - 2676g (2 examples)
Ping Ride 2500g and 3030g (2 examples, but 2500g may be a bogus weight)
Deep Ride 2926g (1 example)
Rock Ride 2550g (1 80s example and seems a bit light)
On my reading of the model introductions and deletions, there wasn't a HEAVY RIDE model during the 1978-1982 period. Somebody else may know more. I still haven't had a chance to work on the introduction year for all models based on all information available.
Yours has a weight consistent with MEDIUM RIDE or possibly DEEP RIDE. Yours does not show signs of the distinct hammering style on the DEEP RIDE, so based on what I see there I'd vote MEDIUM RIDE. As far as the ROCK RIDE goes the one weight I've got seems a bit light, and it has a larger bell than 5.25" as far as I know so that would rule out ROCK RIDE. Unless somebody has a 20" ROCK RIDE and can measure the bell diameter and height for me.
I don't know about any forensic techniques to look for ink which has been removed by polishing over the years. If there were such a technique I'd love to use it to get more samples of cymbals with ink. Once you get back before the 1970s cymbals with ink get rare, and it takes a long time to collect weights for different models.
