I would suggest the same, Or looking into a second hand engine (which if you source it correctly will be ready for your base)
I have an 06 Mulch & Catch here, which I use for my lawns, I was not keen on the 06 Chinese power-torque, so I pulled across the engine from a 95 Craftsman, and put a nice cowl on, now it runs beautifully, and to this day starts first pull.
The craftsman engine was off a mower I got for free!!!
If you really want to swap to a 4-stroke, look for a suitable decent brigs or Honda engine on a base that is not up to scratch, most tip shops can help here, if your lucky, it will be a Victa base, and all the rings etc for fitting will be there.
Otherwise, if you do decide to go with the new engine, i would look for a dead Victa four stroke with the same or similar engine, and rip the ring off it, just be careful of shaft lengths, if you pick the wrong new Briggs engine, you might need 3 rings, and that could be a little precarious!
