Steering worm and gear wheel

[Boston Lodge]

I am looking for a steering gear and worm wheel for an 8" scale Burrell tractor. I have looked at the dimensions of one for a 6" Savage and as the gear wheel is 3.687" across the teeth, it is possible I could adapt this. Has anyone got anything of similar size?
I am in fairly urgent need as I cannot steer my engine at the moment and the cost of having one made to the current specification is prohibitive.
Has anyone got anything out there that I can consider please?