Hi guys. I have an 84 manual iron duke that I would like to do the 3.8SC Swap. I have a cradle from an 87GT. I would like to convert the manual to the automatic 4T65E-Hd transmission. Other than removing the clutch pedal, swapping the shifter and shifter cables, does this sound pretty much straight forward ? Any possible problems or is there anything I may be forgetting ? Many thanks in advance.

You'll also need is to route cooling lines from the transmission to the radiator.
You will need custom axles, custom meaning you'll swap end pieces and shafts. This is well documented on these forums.
As you're going from manual to automatic you'll need to wire up a switch for the torque converter clutch to the brake pedal. The switch may already be in place on the manuals just nothing connected on the TCC circuit.

Nearly the whole car is made for AT or Stick trans.
Like Cabin and Engine Wiring expect one or the other so TCC and Safety switch(es) are right for the trans type.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Not hard to put an auto in a stick car. Just did one.
1. remove shifter and shift cables.
2. unbolt, remove clutch pedal, and clutch pedal bracket . connect lines for safety switch together. Discard Clutch Master cylinder, save cylinder and lines.
3. remove brake pedal and replace with auto brake pedal. It bolts right in using a shorter bolt Use existing brake pedal bracket
3. replace radiator with one for an automatic so that you'll have a trans cooler. (or use a separate cooler)
4. run trans oil lines from auto trans to trans cooler
5. bolt in auto shifter with cable . Connect BU light switch leads that were there together.
6. rewire start and BU light switches to go through trans selector switch.
7. Attach trans cable to shortened and reversed auto trans lever on 4T65eHD

Those are the basics.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 03-16-2020).]