Jeff,
Welcome to the Shopsmith Forum.
The Mark 5 with serial number 379458 would be early 1963 in my estimation. JPG has a Goldie Mark 5 made a bit before that one. If original it would have the Poly V drive and the 1-1/8 HP Motor. It would be equivalent to the 1980's one you previously had although a few changes occurred between 1963 and the 80's. As for the Model it predates other Mark V Models so unless it has been upgraded it would be a Mark 5 with the original Table System which became the Model 500 with the introduction of the Mark V 510/505 in 1985. It is the Table System that determines which Model it is.
Any current upgrades and replacement parts will fit into it. It could even be upgraded to a Power Pro Headstock. There are some warnings in catalog listings like the following one for the Lift Assist saying
Older MARK V units made prior to 1972 have different base castings that require a uniquely designed Lift Assist to accommodate the updated PowerPro headstock. This version is customized to fit those legacy machines that have been modernized.
These warnings have to do with the diameter of the Bench Tubes previously being 1-7/8" diameter as opposed to the 1-3/4" diameter Bench Tubes which actually changed around 1960. It's one of those cases where you need to understand the warning's true meaning and how it actually applies to your Mark 5.
As for SPT's all of them can work on this 1963 Mark 5 as well as they did on your 1980's Mark V.