20psi won't hurt the engine if you do it smart. Intercooler, Pyrometer, additional fuel, good exhaust, properly sized air filter, etc.

Any traditional T3 can serve as a parts source. The T3 from the 86-87 300D/SDL has a 50 trim compressor, the 3.5L engine has a 55trim and the turbo Mustang/Thunderbird/XR4ti have a 60 trim. Larger trim flows more air at a slightly lower overall efficiency.

Check ebay, there are parts on there all the time.