Truck won't start - Where to start?

[thelongrangers]

I have a 1972 C-10 Short Bed that I have owned since 1980. It has 183,000 original miles on it and I have not had to do much to the engine. Yesterday I started it up and let it warm up for awhile as I was planning on driving it later in the day. It started right up with no issues. A few hours later I went to start it and it wouldn't start. When I turned the key, it was cranking, but something didn't feel right or sound right. I could feel a grinding (think it was coming from underneath the firewall). Never quite felt this feeling on any vehicle.

Not sure how or why something would occur so quickly. Any help would be appreciated. I am thinking about starting with the starter, but I have never had a starter fail that quickly. If it is the starter, it gave no signs such as not catching the fly wheel.

Any thing else that could produce a grinding feeling as the truck is trying to turn over?