In my opinion you should run the 70-72 B-body K-member if you are interested in handling. The 66/67 stud mounted idler flexes. The unique 66-67 idler will or allready has been discontinued. The wide 66-69 style sway bar limits the backspace rims you run in the front and they hang down a little low and bushing straps got beat up
Beware,
the 71 and up (newer) K member is totally wrong, the steering box mounts at a different angle, Like an E body.
68-70 should be what you are looking for., but I dont think there is any differece between 67 and 68 as far as engine location.
It also sounds like you need a C body style notch in the oil pan. I think that is the 187 pan..