Yes the '65-'68 power to manual gearbox is a direct bolt in. I think the pitman arms are a little different but most boxes you find will still have the pitman arm on them. The pitman arms look almost identical.
I don't know what other years interchange, but here is a pic of the power box on my '68 so you can compare...
I can get you that part number of my '68 box... Eventually. Not sure exactly where it is, probably in my basement buried in parts for my '68 and '66. I'll probably be digging that box out soon to put it in my '66 unless I go manual from the junkyard. The power box in my '66 leaks profusely out the steering output shaft seal. The '66 convertible is kinda for sale if anyone is willing to pay for it what I have into it, so I may stay with power since most folks probably prefer that. If no one buys it by the end of the summer I'll probably keep it and do manual steering use the toploader I picked up for my '68, since it's a small input shaft and the '66 only has a 289.