The nuclear reactor hatch is especially near and dear to my heart since I've spent years of my life designing and redesigning the various parts as better an better information became available. Our team collectively spent close to 10 years perfecting the design and actually gave Bob Gale one of the first production run parts as a thanks for making the A car restoration possible.
Some of the information that we received on this part is not my intellectual property to share but I should still be able to provide some help. For starters, you can't consider the lid by itself as a single part. It was designed as a unit with the lower 'core' that it locks into. The lid and core collectively make up the "reactor hatch" as it is referred to by Michael Scheffe who designed it.
The core is attached to the turbine nozzle with socket head cap screws, and is concentric with the nozzle. The ID of the core is designed to match the ID of the turbine nozzle. The OD of the lid is just slightly smaller than the ID of the turbine nozzle so it can interlock inside. The outer portion of the core was designed to fit snugly inside the center opening of the hubcap that makes up the top of the nuclear reactor.
Both the lid and core are made from cut to length sections of 6" OD, 5" OD and 4" OD aluminum tubes with 1/2" wall thickness. The OD of the tubes are machined slightly to allow the three sizes to slide fit/telescope within one another. After cutting to length the tubes are welded together and the 3/4" solid rod handle and 1/8" bottom plates are welded in.
There is always "the one" photo that was taken that gives just enough information to figure out a certain part. This one photo for the reactor core was a black and white picture taken in 1986 while the car was on display at Universal in the tram tour queue area. The photo was taken at a point in time where the lid had been stolen, and hubcap w/ core had not yet been removed.
I can't list off dimensions of every part but I can share this screen grab showing a section view of the parts as they fit inside one another.
It took a team of a dozen guys years and years to figure everything out so it is not my place to share what is not mine. Information was also given to our team in confidence from other outside sources so that muddies the waters even further.
Given the sizes of each of the tubes that I described, you should be able to scale out pretty much everything else from there without me giving out actual dimensions. It's the best I can do at this point, sorry for having to be vague on the actual numbers.