So, I was looking through the 15th anniversary issue of thrasher that I have, and I found pretty good sources on the who 5050'd the first handrail:
Gonz interview, page 88:
"Were you the first to 5050 a handrail?
Yeah, I did one at that Savannah contest. Oh yeah, and New York at that Eighth street handrail, it was such a good handrail. It was a perfect height. It was perfect and it was square. That was a good one. I bet somebody could probably do like, a 180 kickflip to nosegrind down that handrail"
Natas interview, page 81:
"then from railslides [on handrails] you started trying to grind?
"Well, Mark was the first one that grinded- this one in New York. He called me up, "I did a 50/50." Then I ended up in New York, and we went to the same one. It was real low, and he was trying to go up it. And I'm like "What?" he didn't really even get on it"
For the record, these were interviews from '96 and they were talking about the mid '80's.
So, yeah, hopefully this confirms that:
-Gonz is pure beast, and a god amongst men (trying to go up handrails at a time when he was the only person who could grind down them)
-And first 5050 down a rail goes to Gonz.