If you have a small listening room and don’t listen loud a properly refurbished 20 should be magical/rich/balanced with the Rogers (dependent upon the preamp used).
I owned Rogers Ls3/5a’s from 1978-1986 and did try them with a refurbished 20 using the preamp/phono section of an Advent 300, and also the phono section of the Advent piped through a Dynaco PAS3X preamp.
In my room (14’ x 22+’ with a 10.5’ ceiling height) there was not enough power for higher SPL’s, but it was fine @ lower listeing levels.
The same was true of an Eico integrated el84 PP amp that I also tried/owned.
I ended up using two slightly modified (choked PS + a few other changes) Dynaco ST70’s as mono blocks instead (the Leak was a loaner anyway from an X-GF’s father).
This said the 20 would need to be properly refurbished, though they are easy to work on (the layout reminds me of the Harmon Kardon tube power amps that came out of few years later).
Oddly enough my cartridge of the time was the Sure V15 III on a Thorens 160/SME 3009 combo (currently still using a Thorens/SME combo, but sold all the Sure’s along with the rest of my gear in 1986).
Never paid much attention to the Rogers integrated amp, though heard them in a few systems years ago (liked the looks of the later model).
DeKay