I ordered a 39" between frame, 1.9" diameter roller(galvanized) from McMaster-Carr (
http://www.mcmaster.com/) - Search for "roller" and then select conveyor roller. You'll find it.
This roller has a 7/16" hex shaft that allows you to fit it exactly between the back of the 52" deck.
1) Go to Lowe's or HD - get 4 large fender washers, 4 stainless steel bolts(w/washers and nylon lock nuts). Also, buy two galvanized steel mending plates (brackets) 6" (I think same aisle). The ones I bought already had holes drilled in them. I just had to make them slightly larger to fit the axle from the roller and the bolts. You need to also buy two cotter pins (same aisle). I think I bought 1/32" or maybe slightly larger...
2) Remove your back 2 anti-scalp wheels.
3) Cut your brackets down to size (I used a reciprocating saw/sawzall) and then if you have a bench grinder, grind/round the end that will be closest to the grass (so it doesn't snag anything if you hit a bump).
4) Line up the bracket with the holes on the deck where the anti-scalp wheels were. Drill the holes large enough so the axle can fit thru it as well as the bolts.
5) Attach brackets to the deck using bolt/washer/lock nut(I can't remember if they are mounted inside or outside of the deck - Just test which way it fits). I mounted two bolts to each side so that the roller axle/shaft fits in the last/bottom hole.
6) Drill small holes in the ends of the axles so that once they extend beyond the steel bracket, you can put the cotter pin in place.
7) Put a fender washer on the axle, put axel into hole in mending plate, put another fender washer on outside and then put cotter pin in the axle hole.
That should be it... You should be able to all this for about $30. It's lasted me all year (of course, I only use mine for my own yard - 1.5 acres). It shows no signs of wearing out yet. If it does, all I need to do is order another $13 roller next year! Much cheaper and same results...
Good Luck....