It took some time, but I developed clear plastic overlays for my screen for the 88's, 37's, wirb, and ostwind. Each one is basically a sight with distance tick marks. The ostwind/wirb and 37mm overlays have lead tick marks too, which while not 100% accurate, they got me in the neighborhood quicker. And it was more of a training thing. I don't use those much anymore. The one I continue to use the most is the 88 flak overlay. It looks like a crazy family of graphs and lines, but I understand it. It shows distance and vertical elevation angle tick marks and lines. Again it's not 100% accurate and is more of a training aid, but I can nail approaching bombers pretty far out, 8k-ish. I also have overlays for the M4 rockets (I never use anymore), and for the 88 firing AP at distant targets out to 7-8k (like a nearby gv field).
Some info on leading came from the internet (mils and sight ring info mostly), but a lot of it was from time spent in offline practice. I'll be honest I'm probably going to keep the actual overlays to myself, but I will be more than willing to explain how I got to the point of having usable overlays. It didn't take me long. Maybe an hour to a couple hours for each overlay.