To be honest, your attempts to salvage these headlights is well meaning, but you may be wasting your time - especially since you seemingly have now lost a major component.
I have removed the reinforcing plate in my day. They used to sell blank headed bolts which simulate the "rivets" originally used to fasten the reinforcement.
In my case the nickle plating was immaterial since my headlight shells were aimed at a truck - and the shells are painted. You don't say but I imagine your shells, if pitted, would be a long expensive road back in plating/restoration.
You can buy shells complete on Ebay. The places to look on condition are at the lower quadrant, particularly at the two "fingers" which hold the rim/glass keeper tie-bar. Also at the top where the slot is for the retainer spring.
What happens is someone goes through a restoration of their Model A, and decides to buy the stainless steel headlights and "do it up right." Stainless IS the ideal solution rather than plating - well except for competition - which is an entirely different ball-game. But their removed headlights end up on Ebay as a way for them to recover some of the cost of new stainless.
My experience is these are usually pretty good. Most seller are honest and will answer questions if there is any doubt. And even displaying an interest in a Model A part of Ebay may result in a lower offer privately from the seller.
I wish I could help more. Some things you just have to let go. All the other do-dads, the glass, the reflectors, the t-bar keeper, the top spring, the bulb sockets all have value if you can clean them up.
Joe K
