>>1808930I used a Vetta rear rack for years. Got it from the co-op for $5. Mine bolted to dropouts at the bottom, seatstay barrels up top. But I've seen plenty of that brand with the central stay for brake bolt mounting.
No idea the exact figure for heaviest load, but I used it to carry laundry to the laundromat, so ~80lbs.
IIRC, the brake bolt scheme is how Old Man Mountain got a foothold in the rack industry. But for the past decade those "p clips" with rubber inserts have been more popular. You can put them on seatstays or chainstays.