Serial number/year info
Serial numbers can be confusing. There have now been 4 separate companies make Mark V's (Magna Corp, Yuba, Shopsmith, and RLF LLC) There have been manufacturing facilities in several cities (mainly Ohio) over the years as well. When SS took over the rights from the defunct Yuba company, several years had passed and records were sketchy.
Some clues to the age of your machine
1953-1960 machines were 2 tone green/cream (greenies)
early greenies had no inspection port access hole nor cutouts to see the gilmer belt. These were incorporated bit by bit over the first few years.
1960-67 Anniversary models were 2 tone copper/gold (brownies)
In mid 1962 they switched from gilmer to poly v drive and changed the motor from 3/4 hp to 1-1/8 hp. You may find a 1962 machine configured either way.
From 1972 on they have been gray. They have used several shades/textures over the years.
1985 changed to 2 bearing quill
Mid 1991 they went to the type C headstock casting with a larger inspection port opening and cover.
Early 1992 they started using the rectangular red safety switch and changed the location of the switch.
Newer machines have a sticker like this for its serial number. The first ones were below the vent plate, and in 2003 or so they were placed on the front of the belt cover below a huge warning sticker.
Earlier machines have the serial number etched on the vent plate surrounding the idler shaft on the belt cover.
Motor types used over the years
The earliest motors on greenies were the 3/4 hp Franklin motor, very heavy duty, last forever.
Then they went to an AO Smith 3/4 hp motor, also very heavy duty like the Franklin.
Later greenies came the GE 3/4 hp motor with a reliable external capacitor and electronic run switch.
The GE "roundback" motors were used in the late 70's and were 1-1/8 hp. They are prone to having cracked motor pigtail wires which can cause shorts, and also were a step back with an internal centrifugal switch which is prone to dust.
This is the motor I like best, the GE "boxback" 1-1/8 hp motor. it has an external capacitor and reliable external centrifugal switch which is quite dust proof.
Shopsmith offered and still sells 220 volt motors for the Mark V. Relatively rare, but I have seen several over the years. This one is a GE one.
Since the late 80's, Shopsmith has used this Emerson 1-1/8 hp motor. lots of problems with it because of an internal centrifugal switch again, and an internal capacitor.In the last few years I have seen them use an Emerson clone from a company called US Motors which I think I heard bought the Emerson brand.