I'm renovating a small shed that was built with 2x4 wall studs on top of 2x6 bottom plates, for some reason. I'm realizing that this will create a problem once I get to the drywall and flooring stages, as I will need to either raise the subfloor, thicken the walls, or cut down the bottom plates to match the 2x4 wall thickness. Raising the floor or thickening the walls present substantial complications and additional costs, so I feel like cutting down the bottom plates to 2x4 thickness to match the existing wall makes the most sense. However this would require making flush cuts at the exact height of the bottom plates (1.5") to avoid damaging the subfloor and floor joists below.
How do I make flush cuts to a fairly precise 1.5" depth as required here?
A circular saw wouldn't do because I can't make a flush cut with it, and a sawzall with a flexible blade would damage the subfloor and joists below the top plate. Could an angle grinder work with some kind of flush cutting blade? Would one of those fancy Japanese pull-saws work?