Just quickly off the top of my head, I believe the 1993 was a "standard" model and the 1983M was designed for monofilament. Not sure what exactly the physical differences were, if there were any.
cool-thumb jump yay-banana USA young guy, according to my trade cataloge #94, the (M) is the new Summit as Brian has sad its for monofiliment line! the new modle is designed especialy for monofiliment line , Machined precision spool with close fitting spool flanges . Takes 10lb test monofilament line OR Larger with ease! capacity - 245 yds. of 10lb test monofilament line. Firnished with reel bag, cork arbor Comfo ring, screwdriver - wrench and Cub Handle DRAG at that time was $18.95) so you will need the extra parts to compleate your reel to go into the box! The other difference on these reels according to my manuqal is( the housing end plate #215M and the 221 m spool, and the 224M back plate. Now young guy, if you will send me a business size envelope self addresed to your self, with 2 stamps I will send you copies out of my factory manuals! My address is ( E-Z ACTION PRODUCTS Company 759 Terra Lane Amherst Ohio 44001-1116-06 atten MILT or Ryan make certain you list the reel you want diagrams for! hope this helps !