It's a good question. From what I've gathered, there were countless big guys who never made it to the world stage. Everyone will have a different opinion on why, but it seems there have been SHWs around for a very long time. The most successful ones were Willard, Carnera, and maybe Firpo if you count him.
It's tough to say, in comparative to their era's Jeffries weighed 220, Denver ed was 6'5+ but didn't weigh that much at his best, Sandy Ferguson is another that's close, Firpo and Valdes could also qualify These guys are pretty much lock ins: Fred Fulton Abe Simpson Jess Willard Primo Carnera Buddy Baer George Godfrey Carl Morris
^ Yes, anyone you can think of. Doesn't have to be world class. Just curious to see how many big men there were back then.
Sweet, I'll try think of more. Look forward to seeing how big a list we can get. Buster Mathis is another
Pretty sure this was just a publicity stunt but this guy wanted to fight Primo. http://www.thetallestman.com/images/ferdinandcontat/ferdinandcontat (10).jpg
Jose Santa 6'7 250lb http://boxrec.com/boxer/28185 He fought a handful of big guys. This could go on for a while lol
Ed Dunkhorst & Joe Mcaulfie both of whom lost to Choyinski despite having a weight advantage that was likely upwards of 50+ pounds
That depends on your definition of what a super heavyweight is. These days its: 6'4" or taller 78" reach or greater 230 pounds in shape or more 2 out of three, with an " almost " on the other I think would qualify.