L bodies need the no longer made shift rod kit but I can send you the the part links if you buy it, they love to rot the floor pans out too. Max boost I'd put to a T1 is 14/15psi.
You are correct 14-15 LBS on stock, That was top LBS on the Shelby cars...But this car isn't stock, basically this is a T2 conversion with forged crank and pistons...20+ LBS Boost no issues and +20 injectors walbro HP fuel pump, and calibration...it's the little things that make the difference :) No rust on this car,,,,floors and rocker, wheel well all like new. The car still had the original exhaust and muffler on it. This is the original paint on the car by the way...