@billpete just caught your post from an alert and I've been off this site for a good while. I tend to listen more in the winter darker months.
Sounds like you are getting there. The Sylvanias might be nice to keep for a good neutral detailed sound. I have a nice matched set of mid 60s Sylvania black plate 6SN7GTs I store and pop in once in a while. For a little more weight and body I'm still running my PSVANEs up front, in the gain stage, the two front tubes. PSVANE had replaced these with a new version and I like them well enough, not wanting to change to anything else, but that's my system of course.
As to your question about which tubes front/rear we chatted about this a while back earlier this year about the gain/buffer stage tubes, a reference here if you still need it. Put your best 6SN7s you like up front in the 98. As for the phone preamp tubes in the 98, I'm no help there as I purposely did not order a phono section in my 98 pre. I'm not sure if you are using the 98 phono section plus your existing [other separate] phono pre, I have no clue. My local audio dealer in business 56+ years has been selling these little external Red color tube phono preamps and most feel they are good enough for vinyl listening, keeping it outside of the main preamp.https://ag-forum.herokuapp.com/posts/2787379
Also worth noting - cables connected to my 98, etc. This past winter I went through another round of obsessive cable comparisons [again, 10th time, LOL], going in reverse direction. I tried more pairs of step-down lower-cost interconnects to see if I could find something of great value to compare to what I have settled back on now. Nope, nothing, after a few months, back to the better cables and the 98 and my SS or tube amps respond well to the better interconnects hands down. Also helps in revealing tube changes. I wanted to mention this because I don't change preamps much any more, my 98 is my baseline preamp mostly past several years. Another thing to test and obsess about if you have not gone there yet. Have fun.