I would definitely agree that a steel or titanium frame is ideal for a heavier guy. We've seen too many big and heavy guys breaking aluminum frames, which is especially lame when you are out on a long tour. Titanium doesn't fatigue like aluminum so things like rack mounts and load points won't fail from the weight and vibration of the gear. A steel fork is a good idea, but we've had good luck using the
CoLab cross fork which is a cool carbon fiber fork with 50mm clearance and rack and fender mounts. We built a few really cool titanium touring bikes for guys who were 6'7" and well over 250lbs and the forks have held up well so far. That fork is compatible with a 203mm rotor as well, which is not common for carbon fiber cross forks. We tried a titanium fork for one tall guy, and it ended up being a little too flexy when he put gear on the front rack. If he was only loaded on the rear, the fork was fine, so we ended up building a steel one for him instead. It was worth the try, but titanium forks are tough because it's hard to bend larger diameter tubes well enough for a fork. Black Sheep Bicycles in Fort Collins Colorado does a nice job with that, but the ti forks are pricey.
Beyond the frame and fork, I think wheels are the most important thing for a heavy guy. Higher spoke count (36h should be plenty, but maybe even 40h), and hubs with robust freehub systems will keep you out of trouble.
I hope that is helpful from a frame building point of view.
Thanks,
Nick Wigston
Zinn Cycles Inc.
Clydesdale Bicycles
303-499-4349