If your tractor has the regular type of transmission, not a "hydro-static", yes, it probably will, if used carefully. If you intend to try breaking of hard ground, or plowing dirt, your Yardman isn't exactly suited for that work. Although, you can try it, but do not be surprised if it suddenly decides to fail, even with the geared transmission.
As for the muffler, i'd say buy the type for the engine!
That way you won't have to worry about back pressure, etc. Mufflers are not expensive, and are designed for correct back pressure, and exhausting of engine combustion (exhaust) pressures.

yeahy shes just a regular foreward neutral reverse transaxle, if she does fail can i just get another one (same fitting same pulley and type but stronger and more well suited?

If you need to go to duals to get enough bite, you're going to tear out the rear axle. Yardman tractors like your are made by MTD and have Transmatic belt type CVT transmissions and use a Peerless 910 differental/rear axle. The Peerless is probably the weakest link in the whole drive train. The Transmatic with its belts will slip before it breaks. Replacement new is about $300+ and there is no "heavier duty" version available.

Yours is a lawn tractor and is specifically NOT recommended for ground engaging equipment. If you put duals on it, expect trouble.