Sequential Tube Monoblocks

I have had three ARC Reference 160 stereo amps and two of the same model monoblocks. The monos produced at least two years before the stereo versions and the stereo versions produced over about a year. They all sounded exactly the same… first when unbroken in, and then when broken in. I have been very impressed how exactly the same they all sounded. The monos had a lower noise floor and a wider deeper soundstage than the stereo, but the sonic character was exactly the same. 
 

So, I’m just guessing it is something unlikely to be of any importance. In theory it sounds good though.

Hopefully, the OP will realize access to a competent tech/shop for necessary replacement of ageing  components/adjustments are the only requirement.

Once done, it will outlast its owner.

I'd like to have the period appropriate Mac amps/pre to go with my 67 MR 71 tuner.

What @tablejockey said is right. With something that old it's more important that each has been  modded or repaired if you will, similarly. 

otoh if they're 100% original, then they definitely need to be from the same batch of parts 

With similar  hours of use.

I wouldn’t think so, I would just make sure they are from the same or similar time period/model/upgrade etc.