Yours is a "typical" Brillion seeder and , surprising as it may seem, shares many parts with the current model. There are "older" Brillions and "newer" Brillons with the biggest difference being that the older has needle bearings in the hubs and newer (1980's?) has roller bearings.
Yours is an older model that I think someone converted to 3-pt hitch but that's OK. Might be factory. The small box has a precise metering system for small seeds such as timothy or uncoated alfalfa and will meter with surprising accuracy. The bigger box is a drop type box and will handle fluffier stuff like rye or lawn seed or whatever with precesion.
I would rebuild this seeder and keep as a family heirloom. Buy all new needle bearings, drive chains and fix or replace any damaged tin. Lube up those small box meters, clean up the old welds and repaint. The red is IH red and the green is JD green. Line up the packer wheels so the rear wheels "split" the groove made by the front wheels to cover seed correctly.
The seed metering chart is probably online and the four page "owner's manual is mostly the same for all models. Yours is likely a "Sure Stand." You should actually meter the seed in a test before a big job--all you do is lift off the ground, fill with seed and turn gears with a wrench.
I would not be afraid to seed up to maybe 50 acres with this seeder since it goes really fast. Other seeders such as landpride--I have owned them all--and they are close--but lesser-- copies of the Brillion but the Briilion seeder is the standard by which all others are judged. There are a lot of these machines around and sometimes they go cheap.
In the midwest it could go for $450 to $650. A new six ft model is almost $5,000. And, brushes are only used for some lawn seed specific units because some feel they meter grass seed (only) better.