There were 3 iterations of the coax antenna terminal box for the BC659.

The first two TM210 and TM211 were electrically similar, having matching transformers built-in to match a coax cable.

These are described in TM11-615 , page11, 12 and 13 of the manual ( not the PDF page #). They say that the cable  CO-282 ( which could be RG8) can be cut to the length, no restriction.

The TM218 has NO matching transformer and connects the radio output DIRECTLY to the coax port. They specify to use the mysterious cg-67/MRQ-2, which is a 9 foot length of some kind of coax with a PL259 on each end which is NOT to be  to cut , The length is CRiTICAL to perform the impedance transformation instead of the transformer used in the predecessors.

The manual uses an AB-15/GR mast with sections ms116, ms117, ms118, which is about 9 foot, closer to quarter wave than half wave the the radio was designed to load.

I tried to reverse engineer it , but it doesn't work too well even with a 95 ohm cable .