You really gotta get with the tape heads, with Myles Astor, Mike Lavigne, and others who are plugged in. One thing is sound. Another is tape handling.
Also your location is possibly important. There are people who supply heads or will relap yours; and others who will work on the decks. If it were me, I’d prefer to keep all that local.
Mike is good to start with since he owns several different machines and could tell you the strengths and weaknesses of each.
I got to hear Albert Porter’s almost virgin A820 with refurbished stock internals and it was wonderful. But he was playing legit old jazz safeties. To me that’s the bottleneck with tape- quality source material that isn’t simply audiophile pap that doesn’t cost a fortune, or involve mystery sources how many generations down.
I’d add Greg Beron, but he’s a manufacturer as well as a remanufacturer of machines, you can reach out to him on your own. https://unitedhomeaudio.com/greg-beron-designer-uha-hq-tape-decks/