160-degree thermostat too cold?

You should be able to run 10.5 on 91, 93 would be better. Whats more important is what your Cranking PSI is, I run 11.25cr on a 360 with J's at 205 cranking psi, i run 20 initial with 30 total, a lot of little things will make it work like a Blocked heat crossover in the intake don't just use the paper felpros they will burn through you will need to add metal over the crossover with these gaskets, valley baffle will also help a bit. also a two or 3 step colder plug than the regular 340 hp plug. 180 t-stat with a good cooling system, no electric fan a good clutch fan. phenolic spacer under carb, electric pump (mechanical adds heat to fuel), insulated fuel lines. fresh air to carb will do a lot. Also its obvious but a lighter car with a hi stall and deep gears will make life easier in my case the demon weights a heavy 3,475 with me in it, 4,400 9.5" stall converter, 3.55. So its possible to run hi compression on 93 but you have to plan for it from the start, take your cranking psi and let us know what it is, if its up around 200 your cam is small and the easiest thing to make it live if the things i mentioned above don't work is to slide in a bigger cam. 408's can take a very big cam and still be completely streetable i wouldn't be afraid of running something like a 570 580 lift with 254 to 258 @.050 intake size cam.