Do not try to fit a different engine. That is one machine that must have the side valve B & S unit with extended camshaft. This is the only engine that will fit properly. As it hasn't "thrown the rod" through the crankcase, it is a fairly straightforwards procedure to fit a new connecting rod, and you are back in business. I bought a slightly earlier Titan, with a seized big end, a few years back. Fitted a new rod, plus new piston rings, as they were worn. I have been using it with a sickle mower attachment ever since, with no problems. Find the part number of the rod, stick that number into eBay and often, someone selling a "new old stock" rod, very cheap, will pop up.