Have a 1950 3800 thats been parked for about 7 years. Owner said transmission is good but I've never driven the truck personally, and am in the process of restoring it. With the trans out, are there any tell-tale signs on a SM420 that I should look for to see if it warrants a rebuild?

Easier to do now while its out, but I don't want to fix something that ain't broke. Advice? Thanks!