Only the 67 Marlin was based on the Ambassador. It was also arguably the best looking Marlin -- it was built on the longer 118" wheelbase, and stretching it out made the roofline more proportional and sleek. Unfortunately it was also the Marlin's last year, and the least were produced. Only 2545 built. It was a bit ahead of it's time, as the "personal luxury/sporty" cars didn't become popular until the early 70s.
The 65-66 Marlin was based on the Rambler Classic, not the Ambassador. Front end sheetmetal was identical to the Classic, even the grille. Wheelbase was 112" (in 67 the Rebel, which replaced the Classic, was stretched to a 114" wheelbase). The car would have had a sportier look had not AMC President Roy Abernthey insist that there be enough rear seat headroom for an average size man wearing a hat! He liked big cars and hats... and really wasn't a good fit to head up AMC. That was realized a few years later after he'd spent most of the money AMC made in the early 60s and he was replaced.