We in the music trade have a saying--"If you don't know how the music goes, play it by ear!" Or: "Hum a few bars, and we'll fake it."

If your engine is a Briggs, the usual muffler placement is to a threaded "nipple" that screws into the block, beside the carburetor. When i have to replace an engine, i usually have to go to a hardware store and buy pieces of threaded galvanised pipe, same size as the one that was on the engine. You can buy elbows, sleeves, and pipe, and then cobble up a suitable wxhaust pipe, and screw on a muffler. Threads are the same.
I replaced an engine last week. Was on a Craftsman lawn tractor. The original engine was an OHV, the replacement was not. When i went to put the muffler on, the kind that fits in front of and below the engine, in a square hole in the frame, the pipe was too short to let it fit. So, i made a patented "Rusty Jones fix", by sawing the pipe in half, and inserting a nice piece of gold colored tubing in between the two pieces. Works great. Looks nice. Doesn't leak or make noise. I have found, if ya want to succeed in this business, ya have to be tricky, and flexible!
And, the hammer is a last resort, to be used only on removing flywheels, or pounding the toes of somebody who wants to watch, and is always in the way! ;0)