where's my door hinge plate gone?

I removed the drivers door on my series 2 to assess what work I need to do to the bulkhead. The metal plate with 2 tapped holes inside the bulkhead that the hinge bolts go in promptly disappeared into the hollow bulkhead door section.

I can't figure out how to get into this area without drilling out rivets which I don't really want to do if I can avoid it.

I guess this might be a fairly common occurrence, has anyone had any experience of retrieving this plate please? (I tried a magnet)

Not sure that it should be a plate. I thought they used j nuts that hold themselves in place.

Standard series or lightweight ? as has been said series should have j nuts that slot into square hole and the lightweight bulkheads have nuts and bolts with a square plate at the top hinge but you can get in the back to retreive it

Thanks for replies, it's a regular 1958 109" 2.0 diesel - not a lightweight, but (I now know) definitely has an oblong plate which should have been retained by a cage. The cage has rusted away and hence the plate slipped down the void inside the bulkhead when I removed the bolts. Using pry bars I eased the inside panel from the bulkhead, dragged it up with a magnet and eventually after many bad words got a hooked brazing rod into one of the holes it and lifted it back into position.

You're no doubt right about the j nuts, It may well have been modified before I bought it, there's a fair amount of filler I'm removing.