engine or tranny replacement, which to do first

Hi everyone,
I have a quick question. I'm about to restore my 66 mustang, and I was wondering if I should have the engine rebuilt first or have the transmission replaced first? The tranny is pretty much shot, and the engine hasn't been on for at least 10 years. Any advice would be greatly appreciated, thank you in advance.

You might have trouble finding a Trans you want....regardless of that you may need to rebuild the engine, but if it looks okay, pop in a batter, check the fluids and all of that, take each sparkplug out and drop a little Mystery oil or something like that into each cylinder. Then before starting it, crank the engine by had....a breaker bar with a socket on it to fir the harmonic balancer bolt. If the engine turns...give it about 7 to 8 rotations then try starting it. This pumps all the fluids in the engine now