I want to see if I can use a round bottom wok on an electric stove (not induction). And I figured would using a solid metal block the width of a large hob work? I figured if it curves up the sides a little then surely it would transfer heat well? But I don't know if there's any dangers with a solid block. Think a wok ring, but solid and curves inwards in the middle (concave, is it).
This sounds ill-advised, not just because it's inefficient but also because it's potentially dangerous.
The choice of metal matters here since different metals have different properties when it comes to heat retention and conductivity. That being said, the best metals for this would be stuff like copper, silver, or aluminum, and those would all be prohibitively expensive to make solid blocks out of (not to mention aluminum might just straight-up melt). That means your choice is down to basically either iron or steel, which in sizes that qualify for the "block" description still aren't exactly cheap.
In both cases, the iron/steel will have an extremely high thermal mass which means they will take forever to heat up. It also means that you need to be extremely confident in how much heat you are putting into them because adjustments during cooking will be virtually impossible. Metal-to-metal transfer of heat is also notoriously inefficient due to layers of oxides and imperfections in the surface resulting in trapped air acting as insulation. And once you're done cooking, you will still have a blazing hot metal plate sitting on your hob which could take an hour or longer to cool off, which is just asking for trouble in a household of kids, pets, or the accident-prone.
In short, with the cost, efficiency, hassle, and safety concerns, I'd recommend just getting a specialty electric/induction wok hob instead: https://www.amazon.com/Oster-2124087-DiamondForce-Electric-4-7-Quart/dp/B08B4243TZ/
It would need really very good contact with both the wok and the electric ring. That would be hard to machine.
For rings that radiate (i.e. ones that glow), they'll reduce the radiant heat reaching the bottom of the wok, and you'd be better off with just a ring that supports the wok, and a fairly flat-bottomed wok. This is especially true for radiant heat sources under glass, which are now quite common.
The only time this idea might be beneficial is with those slightly convex solid metal hotplates that take forever to warm up and cool down. Then even a wok with a flat bottom doesn't make good contact, but contact is important.