I can't imagine what I could do for 10k! If you are serious I will research some stuff and get a vague idea just out of my own curiosity. I'm sure you could do a complete ground up restore or damn near close with that kinda cash if you know how to do the work. If you are going to have someone do it i'm sure your options are still pretty wide open. Cobra swap!? or buy a trashed shell and hide a Gt500 underneath it. You could get seriously unique and creative and with the MN12 to start you are already half way "rare".
Suspension(shocks/struts- coilovers!!!, sway bars, spring heights and firmness, control arms, aftermarket re-engineered entire suspension systems) driveline (trans kit, torque converter, cooler), aluminum or heavy duty driveshaft, torsen diff, fuel system, cooling system, change motor platforms to modern Coyote?.... you almost could for 20k......
Also don't forget safety stuff like driveshaft loop, fuel cell, sub-frame connectors/chassis stiffening, brakes, seats, belts, roll cage, etc....
sky's the limit really. You could do a lot of different build types (drag, corner carver, street) for the budget you listed.