You didn’t mention if your Mirada has a center console in it, or not.
Pretty much all FMJ bodies share the same parts, except the J body steering columns are different from F & M bodes, I hadn’t seen a J body with 3 on the tree column, yet but I’m sure one or two left the factory that way.
The parts different (between automatics and manual transmissions) are:
Brake/clutch petal assembly.
Rod from clutch petal to Z-Bar.
Z-bar and its mounting brackets (column shifted automatics have Z-bar as well – but different).
Rod from Z-Bar to clutch fork (extends from bell housing.
Steering column. You can get away with using your old column if you don’t mind the extra shifter handle – unless you are going back with 3-speed manual shifted on the tree. Good luck finding a 3-speed manual steering column. Most people want the 4-speed anyway. Shifter mechanism and rods.
Floor pan shifter tunnel (welded in).
Shifter and console parts (if console equipped).
Shifter and floor parts (if not console equipped).
Transmission, bell housing and clutch parts.
The transmission (from any A, F, M or J body), bell housing and clutch.
I don’t know if your bell housing will fit/work or not. It should as long as transmission bearing retainer fits into the hole.
Make sure your replacement engine has crankshaft drilled for manual transmission.
As an option, and If you have petals, you can purchase a 5-speed (or 6-speed) changeover kit. The kits run some $ and still require modifications to fit (transmission tunnel and transmission crossmember modifications (cutting and welding) - for these kits are not true bolt in kits.
I was looking at getting a 6-speed trans kit, but ran out of money first.
The quote I got from Silver Sport Transmission (for big block 600 HP/600 TQ Magnum 6-speed, August 2015) was for $6,452.19 (US), using my petals. Needless to say, I will be waiting a while before I can toss my auto out to the curb.
Even with that quote, I still would have to make a transmission crossmember and modify the floorpan, myself.
BudW