K-Frame Bolt Size

I was out kicking around in the garage this afternoon & I have a couple of cheap 4 wheel engine dollies I bought way back that are rated at 750 lbs each.

http://www.homier.com/detail.asp?Se...G++1OZP0Tm1CZCf5uQw3ezGPc&dpt=&cat=&sku=05160

I think I might just build something with wood across between them & set it on that. I just want something to move it around in the shop & maybe out onto the driveway once in a while. I had found some nice pneumatic casters at a farm supply store that were about 10" in diameter that I wanted to use but they were rated at 300 lbs each & I think that's pushing my luck.