Old thread I know, but I just did this. Had a '62 Mullard I61 from Blackburn and tried it in V1. Little to no difference. I asked Beans about it and he explained how these Ampegs use the triodes and what each does (and it's not what you would think as with many amps), and said V2 is likely to produce more of a difference. That's the short version. V2 did--it softened up the highs and high mids a little from the stock JJ.
It was a relabeled Mullard and not a collector tube with a nice Mullard logo so I wasn't out a collector price. I'll need more time with other basses, but I would certainly not get a high dollar tube for the V-4B reissue and think it's going to make much of a difference. Some, yes. A little. Not as much as in either of my Ashdown ABMs. There the difference was without question noticable.
Hope this helps someone.