FWIW, the vendor Pops linked to above, aircooled.net, is one of my go-to sources for VW engine parts. John, the owner, has been at it for years, and knows his stuff. It can take a while to get answers to questions, but his advice is solid. I have never had an issue with anything I have purchased from him, and shipping is prompt. No affiliation, just a satisfied customer.
To flesh out using the gland nut and flywheel prop flange some more. The 4130 larger gland nut options seem like a no brainer.
Will either a 42 or 44mm one still work when using a GP prop hub extension? Without having one in hand it is impossible to figure out the height of the nut, or if a larger socket will fit in the counterbore of the flywheel/ dowel pin area, or not protrude and interfere with the prop extension.
Also, with an 8 pin crank it would seem like a bigger nut is better. It also looks like GP has a regular bolt of some kind for theirs. Do you know offhand the thread size for the gland nut? It measures out around 29mm or so. I have attached a picture.
Hub ID is 2.293 with a shoulder depth of .146 Flywheel center counterbore is 2.570 and .648 deep.
Did my sleuthing yesterday. A 44mm socket will fit in the flywheel counterbore with a little room to spare, so the nut itself will fit fine ( diameter wise) The height of the nut is still unknown for now. I have ordered a 44mm 4130 gland nut to see if it fits under the GP prop flange. If it does, I believe that it is the way to go. Whether you use a 4 dowel crank and flywheel or an 8 dowel, the 44mm nut and washer will provide more contact area than a 36mm one.
Using one of these gland nuts to attach the flywheel flange/ prop flange to the crankshaft, is akin to the Jesus nut on a helicopter rotor hub. You'd better have faith in it. I'm ok with using the biggest/strongest one available. They also say you can torque it up to 400 ft/lbs and red loctite it on some aftermarket crankshafts.
I noted the change from 217 to 400 foot pounds. I still would like to come up with a way of locking the nut. On the shrunk fit prop hub for the pulley end of the crankshaft I used loctite on the nut and put a red paint mark on the head of the bolt and checking for movement was a normal preflight item to check. But, the shrunk fit hub is on so tight I don't think it would come off without the bolt.