For most musclecars and bracket guys it is hard to go wrong with 30w oil. If you park the car outside and drive it when the weather is cold then a 5w-30 isn't a bad idea but if the car is parked inside then a single weight 30w probably works just fine.

I run 5w-30 synthetic in my dyno mules. The lower cold viscosity makes it a little easier to prime them and stuff like that. The straight wt oil can get a little thick on a cold morning.