Ugh, now what?

[markinnaples]

I have a heavily modified '68 Camaro with a built 302 and a Muncie Transmission. Previously when cruising in 3rd or 4th gear, I could hear a deep growl coming from the flywheel/bell housing area. Car ran fine, clutch engaged and disengaged as it should and it shifted without problem; I just heard a different growling noise. So yesterday I tried to start it up, and it emitted a very loud grinding noise and didn't start. I tried just a couple short times to start it but I stopped due to the grinding noise. I have my suspicions as to what it could be but wanted to get the experts opinions from here. Appreciate any help, Mark