I've got a couple of the OP rifles in question. One is complete and the other had the rear sight scrounged from it. The original owner had a G3 without a rear sight and it was cheaper to pick up the Brazilian than get another G3 sight.
One thing about them that many would find a bit disconcerting, is that they bbls were not made for these rifles specifically. Rather they were the Brazilian made 30-06 bbls that were shortened and rechambered. Both of mine, have the threads deep inside of the receiver rings, leaving about 1/8 inch of free space.
Never had a problem with either and both shoot well. Both have minty bores.
The stocks are salvaged M1954 stocks that have been cut down and covered with some sort of resin. They also have a thick soft rubber recoil pad that has been crudely mounted.
They balance well and the muzzle brakes work well to dampen the recoil.
I've seen maybe a half dozen of them in the last 35 years.
I don't think their that rare but many of them were stripped for parts, especially the rear sights. Many were then bubbaed into rather poor sporters. The finish on all of them was very rough matte and parked.
Hitzy, I've never seen one that clean. That stock, looks to have been purpose made for the rifle as well. Neither of mine, have finger grooves.