WV,
I have no idea how many Heathkit 21" color sets made it out but you are certainly right I think in that it was probably a bit intimidating at the time. I was fortunate to obtain a complete owner's assembly manual from an owner of one of these that no longer had his set. Mine has a bad 21FJP22 so it needs a tube as part of getting it going again. I have a good spare I can use. It also has a broken degaussing coil thermister, so the B+ cannot get into the circuit either. Beyond this I haven't examined mine further. It is well built however and it even has a built in crosshatch convergence generator! It took getting the manual to learn this.
This set was offered in two versions, with or without a cabinet. Unfortunately the one I got is without. If I was running a funded TV museum I'd put this in a nice clear Lexan cabinet and call it the "Phantom Colorceiver"!
I've been keeping my eyes out for a suitable attractive cabinet from another set of the same era.
Here is a copy of the magazine ads that were in Popular Electronics and similar magazines for this set at the time. I have the original ad in several of my magazines.
Rob