Sounds to me like a plate reverb, an eventide harmonizer for the doubling effect, and actual double tracks that are there in spots. My guess would be compression on a track by track basis even if it's just the tape compression, and then the entire vocal group would hit some form of bus compression on the stereo bus.

Great vocals. I remember a few songs you sang, with doubles, John,  they sounded damn good.

I heard a few spots in this video that sounded like doubles. Hard to say if it is or which method would be best for you.

Like Kyle suggests, you can do this with a good processor, reverb delay.

You can also duplicate the track, use a processor that will allow you to shape the wave around, possibly flip the phase on it and play with it until it sounds good. Just have to check that the double doesn’t get phasy and cancel out. 

You can also use a different mic for the double and also sing in a different spot of the studio too. That’s very effective. 

Thanks guys!

I'm in rehearsal mode for now, so I'll be playing around with stuff.  It will be a while but eventually I will post the track for you.

 

Thanks again!

-John

 

Right on, looking forward to hearing it!