Cool, I have run Edelbrock cross rams and they do fine, but they aren't a real deep breather. Little different story than the M/T
So the runners, with a 3.25 inch estimate to the head and 1 inch for the adapter added (which is probably conservative for both) using a quick L= ( 72 x C )/N { + / - 3 inches } for wave tuning, solved for RPM.
L = duct length (inches) from Plenum ( the first reflection point) to the back of the intake valve.
72 = constant ( probably derived from valve timing )
C = velocity of sound in air ( this is usually assumed to be about 1100 ft/sec)
N = Engine RPM for maximum tuning effect
11 inch runner, plus 4.25 = 5193 rpm tuned length
13.3 inch runner, plus 4.25 = 4513 rpm tuned length
For giggles
Your 11 inch runner, plus 3.25 (no adapter) = 5558 rpm tuned length
Keep in mind, with airflow, that doesn't mean it dies or falls off, you just lose the advantage of the water hammer effect of slamming a little extra charge into the cylinder. If it flows enough, it'll just keep pulling, but maybe taper off in its rate of increase. Matter of fact, maybe it carries the torque curve a little longer which could be a good thing too.
BTW, what hood does your M/T cross ram fit under and what do you run for TBs and air cleaners? We had to put a Boss 9 scoop on a 67 Mustang, but when we did the Edelbrock cross with two Holleys fit, forgot about that. However it was a bit air cleaner limited and it was only a 410 built to stock CJ specs, heads included, and headers, so not a big HP engine.