I successfully installed wheels to the bottom of my Sanyo 4912 conversion earlier this morning. I did it with about $15 in parts I purchased at my local Home Depot. It's a lot simpler than I thought and I'm happy with how it turned out.
The front feet underneath the fridge are 5/16"-18 threaded stem feet. So all you need to replace the front feet with caster wheels is a 5/16"-18 threaded stem caster wheel. Home Depot sells a 2" swivel wheel from Shepherd Hardwood Products that I used for this project. The original feet had a 1/2" stud and the Shepherd caster has a 1" stud, but I was pleased to find that the Shepherd caster screwed all the way into the fridge. I'm not sure how much deeper you can go but these Shepherd casters where $3.98 each and worked out perfectly.
The back wheels were a bit tougher because there are no pre-existing inserts to screw into. I picked up another set of 2" straight wheels from Home Depot, also manufactured by Shepherd. After looking at the bottom of the fridge there's a perfect spot on either side for these wheels.
There's barely enough room to bolt the straight wheels in place, so I pushed the wheel all the way up to the edge of the bent metal and marked where I was going to drill. I started with small bits and progressed up to a 1/4" bit. Using 1/4" nuts, bolts, lock washers and washers I was able to mount the straight wheels in the back.
You can see it's a tight fit on the inside so be careful marking and drilling:
I thought I finished, but when I put the fridge upright I noticed it wasn't level. Luckily, I bought extra washers and after removing and reattaching the wheels a few times I got it level.
Here's what I used to level the fridge:
Front swivel wheels - One 5/16" lock washer only
Rear straight wheels - One 1/4" lock washer closest to the bolt head, and either three or four 1/4" washers between the wheel mount and fridge
I used four washers on the rear straight wheels when the wheel mount was pressing up against the black of the fridge, the fourth washer accounting for the thickness of the metal that the other half of the wheel mount was fastened to.
I suppose you could use sheet metal bolts to attach the rear wheels, but I felt nuts and bolts were more secure - though it was tricky getting them attached. Also, the three or four washer spacers isn't the way I'd prefer to level the fridge, but it's not readily visible so I'll be the only one who knows.
It rolls quite nicely on my carpet. I'll keep an eye out for 2" swivel caster wheels with a brake, but for now this'll do. My SS drip tray is in the mail and the bar handles are on back-order until mid-September. Thank to everyone for the info and advice!