From someone that has done it both ways, and made my living for decades as a mechanic. Leave the transmission in the chassis take the 6 bellhousing bolts out, and 3 torque convertor bolts out. Split the 2 units and pull the engine separately. You may have to come in from the side on your GP, most engine cranes won't reach from the front because of the long nose on the GP, along with the extra engine setback.
If you look in my signature pictures you'll notice a 69 GP race car, I pulled engines in and out of that car for the 3 years I raced it pretty regularly. Pulling just the engine and using a ratchet strap from frame rail to frame rail under the transmission to support the transmission after removing the engine, works just fine. Reinstall, you can raise the transmission up to meet the engine with a floor jack. It's not that hard to get the two units lined up upon reinstallation, just take your time.
One of the biggest obstacles is getting the hood off , and on of a GP, they weigh a ton. Make sure you have some help. The rest is just unhooking wires, hoses, exhaust, motor mounts, throttle cables, battery cables etc. If you look up in a Motors/Chilton online manual, it will give you each, and every step of the operation in sequence. Anyone that has some background working on cars can figure it out pretty easily.
I always leave the transmission in the car, others will tell you they pull the two out together. Having done it both ways, multiple times, I'm pretty sure I know which way is faster, and easier for me. The more mass/weight you have hanging in the air, the harder it is to move the engine crane around, especially with only 1 person.
Leaving the transmission in the chassis, you don't have to pull the driveshaft, speedometer cable, cooling lines, transmission mount, shift linkage, and many times, the transmission crossmember. No transmission fluid on the floor either, and no refill when you put it back together. It saves $20 on fluid, and oil dry. Your chances are probably 50/50 that you'll end up losing at least some transmission fluid when pulling the 2 units as one. Even if you have a dummy yoke to shove into the rear of the transmission, somehow they slip out at the most inopportune times during the procedure. Cleaning up 3-4 quarts of transmission fluid is no picnic.
It may be good time for preventative maintenance to put a new seal in the front pump while you can remove the torque convertor in the car, but be sure you get the convertor fully seated into the pump if you decide to do this operation before you reinstall the engine. Failure to seat the convertor, can ruin your transmission pump in seconds. You Tube video will show you how to make sure the convertor is fully seated before engine reinstall.
https://www.youtube.com/results?sear...seated+in+pump
Hope this helps you out.
