Hmm, the Jensen Mods, huh? Never thought of them for an SVT. I have an 8 ohm Jensen Mod 12" in a little Airline 15w guitar amp I got a couple months ago. Marshall'ed it right up! I'd love to hear them in an SVT.
If yours has a tube relay, there should be a tube or at least a tube socket right next to the 6146's on the left. The tube relay was done in only the very earliest SVT's and was dropped after the first run. It makes no difference in tone because all it does is allow the amp to come on after it warms up, but it's a pretty cool curiosity. Mine has it, but it definitely doesn't make or break the amp.
Yeah, I read in a few places how they are supposed to be great replacement speakers for old SVT cabs. I couldn't afford the eminence 100 watt speakers. Not 8 of them anyway. I don't know who else makes 32 ohm 10" bass speakers. Didn't really look into it. These only handle 50 watts each for a total of 400 watts which is plenty for the 300 watt head. I think the original speakers only handled 240 watts total so you needed 2 cabs to handle the power. I haven't had a chance to really crank it but I am much happier with these than what was in there when I got the cab. It really sounds great. I also have a V4-B going thru an Ampeg 610hlf cab that sounds great and a bit more portable. I posted pics on page 35 but my gear has changed quite a bit since then. I will get some new pics up soon.