The L has the hollow tubes and the LA has the solid tubes, unless you come across a very early LA, which will have hollow tube frame in order to use up left over stock. The L will have pressed steel rear rims and the LA has the solid cast center with a outer rim bolted to it. One other difference is, the L had a Hercules engine. By the time the LA came out, John Deere had perfected their own upright engine.
If the LA in the NAPA store was restored inside and out and a good job done to it, it is worth the $3500 asking price. Unstyled L's are going for $6500 and up. As for an unstyled LI, you're talking big $$$$$$.
The only down fall with these tractors, if you want to call it a down fall, is the serial number tag was located on the back of the right rear axle, where it was very prone to being ripped off with a foot.