Cheap Engine/trans dolly

I like the ingenuity I'm seeing here. I am going to have to pull the entire drive train and rear end to do some frame/body repairs. I think I want to drop the engine/trans/K-member out from underneath in one piece and store it that way. I'm going to have to rent a storage room because I've run out of room at the inn and my wife's van has to come into the garage for the winter time. I've got two sets of two caster assemblies mounted to 3'x4"x3/4" thick steel bar to build off of. Does anyone have a drawing with dimensions for the support points? I assume you pick up the four mounting points and then an extension under the trans mount? I can measure, but I'm lazy and if that's already been figured out....