Well done for making your own bits Stephen. I know when I’ve made bits in the past on other models, they may not look particularly accurate, but they serve the purpose.
I made my funnel by rolling thin ply, after a good soaking in water, around various diameter bits, until I got down to the size I wanted, then glued the edges and glued re-inforcing strips inside. Like you, I will use small split pins to locate funnel pipework. I just need to find where you can obtain them from. I’ve painted a few bits , but I might change the colours a bit before things are finished.
Looking forwars to seeing how you progress,
Jim.