Tony, the backwards clamp with the (impossible) tightening nut facing to the engine block definitely makes this a DVX 6A or possibly an earlier DVX H6A distributor. These were used on the Mark 5 and Mark VII and XK120 and XK140. However, the advance curves were different depending on the application.
If you take it apart, you will get a better idea what model it came from. You’ll need to remove the three screws that secure the top half of the distributor to the bottom half. Then remove the screw at the top of the points cam and remove the cam. Then lift out the springs and weights. Now you’ll see the stamped number on the action plate.
The number in the photo below means it provides 14 degrees of total mechanical advance (at the distributor) or 28 degrees of total mechanical advance at the crankshaft. That makes it an XK120 or XK140 action plate.
The DVX 6A distributors used in the early Jaguar sedans, typically had action plates stamped 17, giving 34 degrees total mechanical advance at the crankshaft. (However, in my collection I have one action plate stamped 21 degrees - but I suspect it did not come out of a Jaguar distributor.
Tony, I’m almost certain the weights were the same in all these DVX 6A distributors. But different springs, action plates, and vacuum capsules were used for different model Jaguars.
Additionally, the points cams were eventually updated from “standard” to “high lift”. With the standard cams, you set the points gap at .010 - .012. With the later high lift cams, you set the points gap at .014 - .016. If you provide the measurements across the “peaks” and “valleys” of the points cam, I should be able to tell you whether it is standard or high lift.
One reason I asked that question is because, over the years, and there was a few recently, confused and wondering if the drive gear had been assembled 180 out, with all sorts of gruesome engine surgery needed
I say just swap plugs wires and make a note of the situation
However, swapping this cam around would be an easy “fix”
Fiendishly bodgy though, dizzy put together all wrong, be very hard to detect for any future owner or technician (although they may never need to know, as it all should work)
I will double check your pic tomorrow on the cam orientation
If the plug wires are out 180 degrees and you don’t want to disassemble the distributor to flip the points cam, another way is to drive out the pin for the drive dog and flip that 180 degrees. I’ve done it both ways in the past.
I am not sure why pan off engine surgery was suggested, but presumably there must be a circumstance where that is needed to make everything fully right ?
I had to fix a blown head gasket on my first Jag, and managed somehow (dont know how) to assemble 180* out, I think I may have used this list to work out the possible issue and drove the car for about 15yrs with the plug wires reversed
Eventually I took the head off again and rectified it
while I have your attention, is that drive pin tapered, meaning it can only be driven out one way ?