A current Dodge Charger or Chrysler 300 with a V8 would be fine. And a lot more competent than a Dodge Polara from 1971. While we would have used a REESE Dual Cam then, one is better off with a PRO PRIDE today (I have a Hensley Arrow, but the PP is the improved Jim Hensley design. The H/A, if found used, can be refurbished fairly cheaply).
I don't know if there is an owners manual. For the most part one received an information packet with appliance manuals, and some very general info about the trailer and how to hitch & tow.
What is worth looking for is an electrical schematic, as well as one of plumbing. Short of the OM, this will cover much that is critical.
Not sure what is meant by "number on upper front".
Numbers often just had to do with clubs, not with the manufacturer.
As to tail-lights,
GROTE or one of the other truck lighting catalogs may well have an LED combination that will fit the original space. I would look at taillights from the year previous and ALL years past yours. Post the available dimensions for tail light mounting.
1973 Ad
Looks like run/turn on outside, reverse center, and brake/run inside. Reverse lights can be mounted elsewhere might be my approach. Earlier S/L trailers had a big single squared lamp. A problem to solve to get out of the way, IMO, and keep the "resto" problem for a later date.