Its dropping down to 14psi by redline simply because it simply can't flow that much. Above 14psi out of those turbos just results in pumping in a lot more hot air. For that reason 19psi is excessive.
Sweet bugger all as far as aftermarket goes, the engines were Jap/Euro only, so I hope you're happy with fabrication. The turbo isn't a T3 flange, its a toyota flange which shares itself with..nothing. However, if you'd be looking at a custom exhaust manifold anyway with the power you are after.
The big hp TA22 I think you're talking about would have been SIKTOY, can't remember the owners name. It made the power a few times, running a very extensively worked head, complete internals, big to4 with a 60-1 front cover. He also went through quite a few motors. I can't say I agreed with a lot of his setup, but whatever it worked, albeilt for a short time.
The main issues with the motor, is the factory ecu, the factory turbo, and well thats about it. Internals..I dare say be at the point where you'd want to replace the pistons at 350hp.