Welcome to the Forum.
Your Shopsmith Model 10E looks in pretty good condition. It is indeed one of the early Shopsmiths having the serial number 1539. As Bruce said it was likely part of the second order for Montgomery Ward. It is interesting to note that it has the second version of the headstock. The Lathe tool rest is the first version that was soon replaced by a single casting. Most of your Shopsmith has version 1 parts. Being the 539th tool made it looks like the only change was the headstock and if it is steel not aluminum the quill return spring housing. Issues with the first production headstock and the aluminum spring housing caused the first two changes in the Model 10E.
As BuckeyeDennis mentioned above I have S/N 1077 which was part of the first order sent to Montgomery Ward west coast stores/catalog houses on November 15, 1947. I own or have owned 22 Model 10's of which 17 have been restored and 14 resold. It is through there restorations I have learned a lot about them and the changes that occurred during their production.
More about your Shopsmith, because it is an early one it may be desirable as collectible but not as much as a working piece of history. Improvements made to the Model 10's made them better to work with. The biggest improvement, in my opinion, was the change to the metal extension table and Magna must have believed it to since they offered an upgrade kit for the wood extension table Model 10E tools already sold. It included the Metal Extension Table, Table Extension Bracket, the Tailstock for the new table, new version of the Fence with both front and rear locks along with related knobs and parts.
I would be interested in seeing more pictures of you Shopsmith and I believe others would too. Of interest would be pictures the of accessories too. I noticed you have 2 saw blades mounted on arbors and one looks to be a later version while the other looks to be an early version. You have the original 6 rib sanding disk, the original miter and the original sanding drum accessory. Although the 3326 Jacobs Drill Chuck is a good one, it is not the original 33B Jacobs Chuck on an adapter that came with the early Model 10E's.
Mark V 520 S/N 09-11-01 completely upgraded to Mark 7, with all SPT's & more.
Model 10ER S/N R64000 first one I restored on bench w/ Shopsmith metal ends & retractable casters. Has Speed Changer, Model 4E Jointer, Jig Saw with lamp, a complete set of original accessories & much more.
Model 10E S/N 1077 oldest one I have restored. On bench w/ Shopsmith metal ends & retractable casters.