I'd get a Victa two stroke mulch and catch ready to go. I think (but not sure) you need to add a plate for the mulch plug underneath the base and I am not sure you can bolt a four blade disk onto that boss. You need the proper mulching disk which is round and has flaps cut into the disk as well as carrying four blades.
Not worth the trouble converting imo.
Sounds like a self propelled mulch and catch would be ideal for you.

Ahh, if only victa had kept producing the thumblatch catcher series, they would be in better shape today!