Sorry, but I have not tried the newer Jensens. I have heard they have a more modern performance and enhanced mids, but I cannot say. I do have a lot of experience with speakers and cabs. I will say for a Marshall sound I use Birch for the cab/ 3/4 and 3/8 for the Baffle. Only put 1 inch foam in the corner of the cabs.
I have built all kind of cabs, but my favorite fro Marshall is a Replica size of a Fender Bassman with the center panel, still made of birch with removable port on the bottom of each section and the back in 3 sections where I can have completely closed, 1/3rd open, 2/3rds open or completely open. Also porting on each. I make the cabinet deeper though. 11.5 inches deep.
On this type of cap with 12's the ports will be 2 on each side which are 2.5 high x 13.5" wide and 7" deep along the bottom. This adds to the height. I do not know the measurements off the top of my head, but if you are interested I can make measurements.
My speakers of choice are Altec 413's, but today are very expensive. The only reason I have not tried Jensens is I don't know where to get parts to recone and I like speakers that generally are expensive. For instance, I have a few Celestion Blues.
I do have the same cabinet with 2 Celestion Golds I use with my 50 Watt Plexi. I run it ported and closed back and it kills, but remember with birch in a 1 12 or 1 12 you really need some sort of cab filler. Even good old fiberglass insulation works. I have simply sprayed adhesive and glued it to the corners inside.
I do the same with pine cabs in closed back, but it is not as necessary. To get the real chest pounding Marshall crunch, IMO birch is the only way to go. If you make you ports that you can close the cab will be more usable in a smaller room.
really the old Jensens were economy speakers, but I just do not feel the work Marshall and Jensen go together and I am really not a fan of the older Jensens except for the ceramics they used is some of the early Super Reverbs, but even them I prefer Weber 10A125.