Is your rear sway bar a factory bar or aftermarket?
When rear aftermarket sway bars were available (many many moons ago), many were sold without any hardware - which makes for a useless part. If memory (is still?) serving me correctly, at one time, there was three different companies making/selling FMJ sway bars. Of those, only one (of the three) sold any mounting hardware. Those have dried up decades ago - but Firm Feel Inc has recently made sway bars for FMJ - with the hardware (yea!). Firmfeel Mopar Suspension and Steering
I would "guess" they might sell you what you need (less the sway bar) . . . maybe.
FFI is the only company I have seen that offered anything larger than 3/4". All of the other aftermarket companies (and Chrysler) were all 3/4".
I have a set that I removed from a '84 Gran Fury police car that I can get measurements for you. I wasn't planning on selling it (or parts thereof), BUT if someone is willing to give me money I can put down for an 7/8" FFI unit, you might have my attention (...or maybe not).
The shock plates is the biggie. I think making your own adapter plate might be easiest - maybe, like this:
I have the frame mounts, from Firm Feel sitting in the garage. Hadn’t put any thought into selling them before.
I have factory AHB frame mounts, AHB sway bar with Firm Feel pivot bushings, end links and M-Body link mounts (you have to weld the link mounts onto your stock M-body shock plate like it would have been from factory) on the car at the moment.
The Firm Feel frame mounts are supposed to be “universal” for A/B/C/F/M/J Mopars according to, Frank from FF. Meaning that the, Firm Feel mounts don’t locate to or use the factory frame mount bolt holes that come on our cars from factory; you’re supposed to Swiss cheese your rear frame rails and drill new pilot holes and secure the mounts with self tapping bolts they supply with their sway bar kit when you buy it...mine didn’t come with the self tapping bolts (which is what started the email on how to mount them) or any kind of printed instruction or product details and they don’t list any of this info on their website product description.
Maybe give them a call and work out piecing an order together for the parts you need/want. They’ll work with you on that for sure. Plus, you’ll have the chance to decide on the weld on M-body end link mounts or the B-body end link plates that, @BudW recommended; But, you’d also have to switch over to B-body shock plates and shocks to use the B-Body end links plate because they’d replace the factory M-body shock plate all together...as to the M-body link tabs just welding onto your factory M-body shock plate. However, the B-body rear shock plates would give you way better options for shocks to get the most out of your suspension...but more money.