The bulb I have in it is yellow and has two contacts. The bulb I need and would be the same as the spot lamp has single contact
Would not a yellow/amber indicator bulb do then?
I am sure you have looked into this deeply and whatever the problem is the solution isn't easy, or you would have solved it.
For the last kit car I am supposed to be building, I bought a pair of P80 headlamps. They are exactly right for the car, but they are so old, that their dipping mechanism is to switch the offside one off and mechanically move the whole reflector, bulbholder etc down and to the left, with a solenoid. so there was no way I was going to be able to pass the MOT like that, as this was pre SVA this was all I needed to register it.
So I got hold of some Volvo sealed beam units that would fit inside the P80s and spent ages converting it all to fit. It worked and the P80s still looked like P80s so I was happy.
Since then I met a bloke with a real Jag SS100, and we talked about this issue. In his case he owned an engineering company (he had so many old Jags it was unreal!) so he was able to get his staff to take the back out of each reflector and spin metal up etc until they would take modern two filament bulbs. A much neater solution. I suppose I could still do that, but I have so much more to do on the car that this will have to wait.
This is why many owners/builders of 30s style kit cars fit aftermarket headlights, the sort you can get for Lotus seven copies, where they look like spotlights and keep the bigger ones for decoration. Provided they go where the regs say headlights have to go, they are OK.
So I do understand the problems one can have.
Replica Owleye rear lights are a heck of a price. He had two, so used them for indicators and rear/brake lights. I could not afford that so I got one, to act as fog, reverse and number plate light, and two others of a different type for the indicators and rear/brake lights.
Sorry, I am rambling!