Bob,
I have not seen Utah speakers in a Sunn cab before......Jensen, Eminence, JBL, Cerwin Vega, Magna (by Eminence I think) yes, but not Utahs. You will hear an improvement with the JBLs!
I've had good success cleaning Sunn tolex Like this......spray the tolex with a household spray cleaner like Fantastik, 409, etc. and let it sit for a minute or two. Then scrub the tolex with a stiff nylon bristle scrub brush. The cleaner will turn a dirty brown color. Then wipe it all up with an old bath towel. You will be amazed at how good the tolex looks. Do the same with the grille cloth (removed from the cabinet so you don't get the speaker cones wet), but use a soft bristle brush judiciously.....go very light with the brush and wipe it up with a towel.
Good Luck!