The biggest difference is the hammer spring. On a M62, it is a traditional flat-spring, and on the M62A, it is a modern coil-spring.

Bert

28 gauge said
 Thanks for that Bert.So unless one looked inside or at the serial number ,you cannot tell them apart,just by looking at them.  

No, there are several other visual clues, starting with the marking on the barrel.  Most of the Model 62 rifles had the small (short) slide handle stock, whereas the 62A has the longer stock.  Additionally, the exposed portion of the lower tang on a Model 62 looks just like a Model 90, whereas the Model 62A has a completely different look due to the lack of the screw holes for the flat-spring.  In total, there are a number of visual clues to quickly tell them apart.

Bert