If he already did the upgrade and had it running then all you need is a 2.5r OWB.
They are easy enough to replace, four screws hold the motor in and the throttle linkage, ez-start wires & fuel line, of course. Then four screws take the ez-start off, then the old bearing just slips off the shaft. My only tip is to be sure you note which way the old OWB grabs/freewheels so you get the new one on right. If memory serves the OWB's are not marked to distingush directions. Go ahead and pick it up, they're fun trucks.
Dave