I run Wix filters in everything. When you look the parts up on MTD's or PartsTree web site take the KB part number and cross it over to Wix, NAPA or something else. Do not use anything but IH HyTran oil in the rear.
You may have a new drive shaft but there is a brass insert on the motor end, coupler on hydro pump input and 2 rag joints at each end of the shaft. If you run the engine WFO and don't have a lot of vibration on the tunnel cover you are probably okay.