San Juan Car Co. has been producing kits and detail parts for O scale modelers for many years now. A couple of years ago became interested in Proto:48 and bought their Bettendorf truck kit to get a feel for the gauge.
The trucks are incredibly detailed and have very little flashing to remove. Brake detail is also included. The side frames have raised lettering, which is crisp and easily readable. Like most of their smaller kits, the instructions are on the back of the packaging, which are well illustrated and easy to follow.
Putting them together is fairly easy. The bolster is the only part of the truck superstructure that is glued. The rest is held in place with gravity as on the real thing. You will have to glue the brake detail however.
I am not a fan of the plastic springs or the wheels that come with the kit (they still are very good quality) but there are some manufacturers out there that sell replacement parts for them such as ProtoCraft and Mullet River Model Works.
SJCC does make an O scale version of the truck and you can expect the same type of quality.
If you are looking for a low cost way into O scale, this is the perfect start and a great one-night project.