Dear Andy,
NJ International and NJ Custom Brass were brass IMPORTERs by the name of Nick Reiss and Jack LaRusa.
NJ is NOT New Jersey but Nick and Jack !!
In fact the business was run out of Long Island
i also believe they are still in business selling signals.
KTM stands for Katsumi Models and they sold there products through various IMPORTERS in all scales.
The GP-35 may be a US Hobbies IMPORT
whose builder was Katsumi Models.
I am not aware of the NJI/Custom Brass builder as they dealt with 4 different builders in Japan and later Korea.
I have found the KTM drives to be OK if well maintained.
The NJI / Custom Brass drive units are a bit of a crap shoot.
Brass train collecting is great and books have been written by the various collectors and welcome !!!!
John P Dunn Sr. President CVMRR