When I had my VT200 I bought non ARC SED 6550's from a well known Canadian tube seller and found the pin diameter was slightly smaller than the ARC SED tubes. I had one arc, and it cost me $500 shipping plus repairs to send it back and forth with ARC. ARC does extensive burn in and matching on their tubes.
I did use the new issue Tungsols in a VT100 mk2 and found them reliable and good sounding. I also used SED KT88's in that amp without a problem.
The problem as you probably know with the VT200 is the HUGE power supply, which even though a dual mono design takes all the current from both channels through an arc'd tube, taking out a resistor and some traces. They make them that way for the best sound quality, but it is perilous to use questionable tubes.