Ask the experts, I say....

So here I am. Have a Snapper Hi-Vac self propelled mower P21500 B&S 5hp engine. Bought her new in 92 or 93. She has served me well. Have replaced belts, drive disc, blade, plug. Rebuilt carb. The engine is shot. As we will all agree, they don't make them like they use to, so I want to replace the engine. I am not a mechanic, 60 year old 5'2" woman who learned a lot from my late father who sold and worked on mowers. My question....do you think this is something I can do myself, or am I better off leaving it to the professionals? I know I have to measure the crankshaft to make sure it will handle the self propelled.....the self propelled part has me concerned. Not sure I have the right tools! Borrowed a mower today, but will need to mow again for sure. Whatdaya think?

Thanks for your opinions!