dajonx- Be a little careful about using non-automotive products.
I just finished the initial cleanup of my Crown Vic's wheelwells (eleven years of previous-owner neglect). It's usually not all *that* hard to get things OK. My suggestion (I'm assuming you're not using a steamer and/or pressure washer):
-jack car up and pull off the wheel
-get some good lighting on the subject so you can see what you're doing
-rinse thoroughly to get all the loose stuff off
-spray on APC and let it dwell. Agitate with a brush
-rinse and inspect
-use solvent to remove tar
-if there's paint in there, try the solvent and gentle agitation with something like a plastic razor blade or a piece of plastic or wood ("chipping it off" approach). Be careful with solvents like lacquer thinner, often/usually OK but you never know
-rewash with APC
-use polishes/paint cleaners as needed to clean up what's left