Yep, a 66 is definitely the NF. The PF cabs are very cool, but while they do have similar tones, they go considerably lower than the original cabs. I'm a bit of a purist when it comes to the B-15 sound, and I would only want to match it up with an identical cab. You might find an orphaned cab or www.fliptops.net
makes repros. Vintage Blue makes great stuff but they only make the double baffle cab, and not the single baffle like you have. Load it with an Eminence Delta 15a and it'll sound identical if you have the original CTS speaker.
An alternate plan is to unbolt the head and bring the PF410hlf by itself. That might work out well for you if you want a cab that goes very low.