Hey speedwagon, welcome to classicbroncos.com!
Unfortunately for avid readers, there are very few definitive answers to anything involving Early Broncos. There are just too many inconsistencies from the factory, and more important too many inconsistencies among us doing the building, swapping and driving for there to be just one correct answer for all things.
But yes, for the late model 302/5.0 you need the 50oz imbalance flywheel, and also the matching Explorer/Mountaineer damper. Assuming you'll be running the Explorer front accessory drive that is?
If not, you'll need to source the appropriate damper for your belt drive system, and possibly have it modified to work with the 50oz engine.
Company called Damper Dudes can help you if it's not a commonly available part.
For the flywheel, any later model manual trans Ford truck with a 5.0 will work. As long as it's got 164t ring gear, and the bolt pattern for the clutch you want (most should fit that bill) you can use it. All the crank bolt patterns were the same from what I remember.
The #8210 on this page:
https://www.wildhorses4x4.com/category/Early_Bronco_Clutch is that type.
Most, if not all later flywheels are working with the clutch bolt pattern for a diaphragm style clutch, rather than the original 3-finger "Long" style our trucks came with from the factory. Some (like the ones we sell I'm pretty sure) will have the pattern for both types, but usually swaps involve aftermarket clutches which are diaphragm style more often than not anymore.
Good luck.
You changing transmissions too?
Paul