I have an older OS Recto 412 that had the 70W Celestion V30s. I did not like them with any amp. Too flubby or it would get stuck in a horn like sound. I swapped those out with the EVM12L Black Label speakers. OMG did that make a world of difference. The JP2C never sounded better. Even ran it with the Mark VII. Comparing that to the standard 412 with the current V30, the EV loaded cab is much louder. I have been using it with a Roaster for some time. I had the cab apart so many times the screws could not be used to hold the grill in place. So I used the metal gromets and screwed the grill from the front through the frame. Also added some weather stripping to prevent the grill from vibrating. The EV works really well in a sealed 412 cab. I needed longer screws for the speakers as the original screws were too short. The grill did not permit front mounting the speaker and I did not feel like taking a router to the frame to get the clearance. The few extra pounds of the EV compared to the V30 is not much. Cab weighs enough as it is without any speakers loaded.
Also loaded up a Mesa widebody 112 cab with the EVM12L classic. Sounds much the same as the black label version. That was one of the first cabs I wanted to try out with the Mark VII. WOW, the clean channels were epic on their own. Gain modes were also awesome. As for the Mark V90 in the image, that speaker is an OTR (Organic Timbre Rhapsody G12F) which has more of a treble roll off than the EV. Was hoping that would help with the ice pick tone of that amp.
Conversion of the combo to fit an EV is not simple. Mounting the EV like you would the MC90 is not possible, it leaves no room for the chassis, clearance of the power tubes and or tube shields cannot be removed unless you pull the chassis. Note that this is a widebody Mark V90 combo shell. I first tried rear baffle mounting, was not going to work out. Sanded out the speaker opening with a round drum sander, so the speaker frame just fits. The OTR was a little larger than the EV. No T nuts, just washers and cap screws and locking nuts. The cap screws will embed into the frame of the speaker so they basically lock in once you get them seated. #10-24 is what I used. Pictures of swapping the OTR to the EVM classic so I can compare a better apple to a lemon.
Modifying the frame took some patience as you need to remove some of the wood to get the speaker clearance at the bottom and top areas. I did that with a router and lots of luck but managed to keep the frame from breaking in half or cutting off my fingers during the process. Sorry I did not think if taking a picture of the grill from the back side. In my opinion, the Mark V90 is not very compatible with the EV speaker. However, never threw a dust cap with it like I have with every MC90 I tried. As for mod to the Mark VII combo, not sure if it is possible due to the frame of the grill and the resistors mounted to the bottom of the chassis. Not sure if the small fan will be in the way or not. It may fit but doubt it is possible with the EV mounted on the rear side of the baffle.
If I ever got tired of the Mark VII and JP2C heads, I would buy a Mark VII combo shell and modify them for the EV speaker as the JP2C chassis is much the same as the Mark VII. Just does not have the two resistors up front since the speaker off load resistor is internal on the JP.
In my opinion, EVM12L is the way to go for the JP2C or the Mark VII. You can go all out with the EV. Besides, that is what was in the Mark III combo I had. Plenty to fit in the mix of a band as that is all I had during my band days in the 1990's.
Open back or closed back, the EVM12L can do it. You basically get out of it what you push into it.
but... there is a thing I discovered, it's called the scroll bar. If there is some verbiage I'm not digging I'll just use it to "scroll past it". Works really well. 
