Another perspective is to grab good iron when you get the chance. If your acquisition price is good, you should be able to breakeven when you eventually find your holy grail.
Plus, the sooner you get it, the more years you will get to enjoy it. I had that epiphany when I was getting near 30 - a tool you'll use all your life is a tool to buy sooner rather than later.
I recently lucked out on a really nice 1969 1408 AVS in the 30" size. It's about 7.5' long, so the 54" version wouldn't have made it all that much larger. This happened near the end of a long active search for 10EE, when I was in the inspection and negotiation phase. So the timing was awkward. I arguably didn't need the 10EE after I got the 1408 (especially given how tight it is). But, ya know..
The AVS isn't powered yet. It is in apparently great condition. The story of getting is pretty good, and I need to write it up. I'm still evaluating/cleaning it and the 10EE. I need to decide what to do with the 480V Reliance DC drive (Cardpak). The Reliance nameplate even has some key fields filled with only "Special". The drive is apparently simple in many ways, and yet not - the very large cabinet is jam packed, and I don't have a schematic. Used parts seem pretty cheap, and it is fairly modular. I am fortunate to have EE friends who are into old ham gear and fixing oscilloscopes, so they should be able to help with board level work. Still, there are a great many adjustments in this system and I don't know anything about setting them.
Much like a 10EE, I worry that the easy path to an AC VFD retrofit would result in the loss of original performance. Though that might be something to do on a temporary basis.