The Spitfire and TR5 were very different vehicles with very different power plants. TR5s used an Austin-Healy sourced six-cylinder that had no relation to the Herald unit.
Amphicar used a Herald engine which was also used (in modified form) in the Spitfire. I believe the earliest Spits, Heralds and Amphis used the same 1147cc unit, with different carburetors but the same oil pans. However, over the years, Triumph made several variations of that little motor, in 1147cc, 1296cc, and 1500cc forms. They continued to change the intake, exhaust, carburation, cam, bore and stroke for almost a decade, ending with a high-torque, low-rev 1500cc version. I don't know if the late-model pans are the same; it could be, if nobody's modified a 40-year-old sports car. So: it really depends on what you've got!
Spitfire pans are different inside. Ours have a screen half way up.
Spits do not. But if you are installing a new replacement oil pump this screen has to be removed or altered anyway.
I have both in stock,