Rebuilt 360 ?

I picked up a 1972 360 with a 727 this weekend for $50.00. No kidding....$50.00. The motor has been sitting in a garage since 1984. When I started to tear it down today I noticed a few things that made me think the motor had been rebuilt before. One thing in particular. What appeared to be blue RTV in the area of the distributor. Any suggestions on what to look for to be certain if it has been rebuilt or not? The previous owner knew nothing about the motor.

Thanks