Looking at a set of AFR 195 LT4 heads, and am building an E85 stock shortblock engine, so I need the most compression that I can get. Anyone know how far these heads can be safely milled down?

I can't answer your question directly, but I have a set that were set up with 58cc chambers, so AFR mills them down quite a bit for that and the first time I had them cleaned up for a rebuild, the shop had to relieve the valve seats just a touch before throwing them on the grinder so, if I were you, I'd get thinner head gaskets and/or higher compression pistons, and make sure your deck height is minimal or figure out some combination that you like which will bump the compression for you.