Tube rolling with Quicksilver Mono 60s -- from KT77 to KT88? KT 120? etc.

Not in my manual. Perhaps they're equivalent?

No they are not! An equivalent tube to the 7581 is a KT66 or a 6LG type of tube!

To adlib on the advice given,
The Person offering advice, is a very experienced owner of Tubes with access to Tubes from a Two Generation Collection.
This person has always been supportive to make Matched Tubes available for loan, and offered much valuable guidance.
The Person has been instrumental in helping others create a understanding of how Tube Rolling can influence their systems.

The advice made available to myself relating to my Monoblocks was to undertake the investigation to learn what was the best Input Valve configuration to get the best from the resident Output Valves.
This is what I did and it has proved so far to be a very economical approach, if the Pre Amp Purchase and Build is deducted from the £700

I felt more compelled to further investigate the Pre side of the System as a result of the impressive improvement to the Sound Quality being experienced 

I see. I listed the tubes my amp can handle, that's why I'm asking. 

6L6 are all over the place for sale. Brand new and matched, about 115 for a matched set of 8. DON'T buy them.

IF they are Solvex, (the older solvex) it is night and day in sonics, and how long they will last, they are outstanding.

The old GE and RCA, metal cover 7581 valve.. serious valve there, super high plate voltage. REAL high, and will stand up..

The 115 sets of 8..LOL Just a bad place to even start.. :-(

WHY? Out of over 150 valves I bought in 3 lots, none of them were at 50% of the TRUE industrial 7581. Closer to 15-30% NEW.. OK, NEW..

Just under a year ago I listened to an MC240 every day for just under 3 years. I used industrial, RCA 6L6 mil/spec metal tube.. They still have 50% wear left on them.. I took the amp down for it's first EVER major service.

This is so fun, chompin' on my turkey sandwich. :-)

Regards