Dr. J has him on his all-time team as 6th man capable of playing guard, forward and center
20 Second Timeout: Julius Erving's All-Time Starting Five
In 1968, one season before the NBA finally let him in, his talent was well recognized by professionals and coaches to be in the company of Baylor/Robertson/West/Russell/Chamberlain even though most basketball fans were unaware of him
Because of youthful indiscretions, Connie Hawkins, who - 12.16.68 - SI Vault
I still can't find any of his wingspan measurements but I managed to find that his hands spread 11" thumb to pinky and I have two different sources that describe his hand length, one says 10" the other says 11".
So his hands are:
~10.5" wrist to finger
11" thumb to pinky
Compare to Shaquille O'Neal's:
11" wrist to finger
9" thumb to pinky
His listed height of 6-8 is probably close to his height w/o shoes given the era he played in so that'd be about 3" taller than MJ, or 1 inch shorter than Kevin Durant - he had a big frame for that kind of fluidity. Listed info says 210 on basketball reference, 215 on NBA.com, and sports illustrated 1969 described him as a 219lb NBA rookie. Like Wilt and Bill Russell he was better at Track and Field in his youth than he was at basketball. So he was a decent athlete too.