I'll see your rusty old truck valve cover and raise you an oxidized fuel pump block off plate.

We made 696 hp and 600 lb-ft with the 465 inch iteration of Gary's TP. We are adding over 40 cubic inches and 10 more degrees of camshaft duration this time around. I think he's going to be in Toploader-splitting territory if he gets a good hard launch.
It's more of a logistics point now....if he busts the Toploader, he's gonna end up with a busted Toploader and a clutch he can't use anymore.
I have built the face plated Toploaders and although they are stout, they are not nearly as street-friendly, nor do they have the overdrive, which would be nice with a 3.91-4.10 gearset.
This build has evolved from a hot street car deal to a hotter street/strip deal. I think if Gary plans to do a little drag racing, the Street Twin should be ditched for a Soft-Lok or similar adjustable pressure plate. It's just hard to get a combination that works really well in both scenarios with this kind of horsepower.