My guess for the Red Hulk (sorry, I ain't calling him "Rulk." That's just stupid. And not even awesomely stupid) . . ? Colonel John D. Armbruster!
Ah, the collective gasp of recognition is deafening. "Who?" you're all asking. He died (or did he . . ?) in Incredible Hulk #185 (1975) stopping an exploding Glenn Talbot (he was an "organic bomb," y'see) from killing the president. BUT! Talbot is now back, as is Betty (maybe the ones that died were actually Skrulls! Yeesh, I hope not), so why not this guy?
Armbruster was another career military man, who had a mad-on for the Hulk. He even took over Project: Greenskin from General Ross, and was instrumental in stopping the Russian terrorist attack by a mind-controlled Major Talbot. The Red Hulk is a military man, a strategist, familiar with weapons, had a rivalry with "Thunderbolt" Ross, and I think he may've once been involved with turning people into gamma-powered monsters. And he died, supposedly with Talbot, in heat energy pit thingie (it may've even been a volcano; I can't remember), which combined with Talbot's "organic bomb" explosion, could, in fine comic book logic, explain how they survived, and Red can absorb energy. That ability, and his military & anti-Hulk background , could've made him a great candidate for the Intelligentsia's "create-a-Hulk" experiments.
Either that, or Red is really Uncle Ben.
We're supposed to find out in June, if any of still care by then. Meanwhile, it's already slipped who the Red She-Hulk is, but I won't spoil it here, in case you haven't heard. (. . . Maybe it's an alternate timeline Aunt May!)