Osco Exhaust Manifolds Identification

[76SeaRay]

I have a set of manifolds and risers that are supposed to fit my 1996 Mercruiser 5.7L engine. I haven't been able to find these on the internet and would need to know what gaskets etc to get for them. They both have the Osco logo cast into them.

Here is how they are marked:

Manifolds -- #120429, 7114B2T and #120502, 7114B2T

Risers -- #112509/1, 8503A and #010611/1, 8503A

Can anyone confirm these and how to find parts (gaskets) for them?

Thanks...