Audio Research VS60 amp Matched tubs

I don’t think you can do that. Your amp uses 6550 tubes. You can give ARC a call to confirm this! Here is the manual!
http://www.audioresearch.com/ContentsFiles%5CVS60%20Manual.pdf

It's EXTREMELY unlikely you will damage anything by putting KT120s in that amp, as there have been zero reports of any issues from switching to 120s which, in my and many other's opinion, are much better sounding than any 6550. You can use KT150s also by the way…no reported issues anywhere…go for it…live on the edge!

My hesitation is whether the amp can take advantage of higher heater current draw of KT120/KT150 and potentially shorten life of the transformer and power supply.

If I have an expensive amp, I would contact the manufacturer before rolling.

Thank you very much everyone for your inputs.  I will call ARC regarding KT120.
Eddy