A few years ago I built a stone pedestal and built a cob pizza oven on top of that pedestal. The oven lasted a few years but due to our moist environment, cob was probably not the best choice of materials.
The oven recently collapsed and I'm looking to now build a new oven (36" Pompeii style) with brick.

I'd like to reuse that original stone pedestal as the base for the new oven. The pedestal is roughly 49 inches X 45 inches (top view). I've read building a 36 inch Pompeii oven should require a surface on which the oven sits to be 59 X 70 inches.

My question is, if I pour a 59 X 70 inch concrete pad on top of my stone pedestal (which is roughly 45 X49 inches), which would produce a roughly 7-10" overhang around the stone pedestal .... would that be courting disaster, having that overhang? I'd plan on making the thickness of the concrete pad about 5 inches and loading it up with 1/2 inch rebar.

Thanks very much for your insights/help.