Original Supra trailers were made by a company called SMP (Sweetwater Metal Products) There really is no information on them.
What you have on your trailer is pretty standard still today but yes, you will have to figure out what size you have. Most of my SMP trailers have 14 inch rims from factory with 5 lug, 4.5 bolt circle diameter. Tires are ST205/75R-14

Your bearings and races should have numbers on them once you take them out and clean. Just replace with identical.
Here is information off my '83 SMP trailer.
Inner Bearing number - L68149 $9.99 @ Northern

Inner Race number - 68111 $7.69 Napa Auto Parts

Outer Bearing number - L44649 $12.99 O’Reilly Auto Parts

Outer Race number - L44610 $5.99 @ O’Reilly Auto Parts

Grease seal - National #473317 $14.99 O’Reilly Auto Parts
Inner Diameter, 1.687”
Outer Diameter, 2.325”

As far as brakes, measure to find the match on eTrailer. If it were me and I were redoing it all, I'd get rid of the hydraulic and go with electric brakes. If you're just replacing a few parts, then stick with it.



MySupra, I use IMGUR.COM for pics. Get you a free account, upload pics, copy and paste the BB Code (message boards & forums) Easy peasy, thick and cheesy.