OK, turns out I was able to order in some Novarossi glow plugs and head shims. As I mentioned above, I'll be running this at 5000 feet with Werks 30% nitro.

Based on what I've seen in this thread, it's appropriate to add 0.2mm in shimming for 30% nitro in a 12-3SCT. My only challenge is that I was not able to obtain 0.1mm shims, I got 0.15mm shims. So I can either add 0.15mm or I can 0.30mm of shims. Any thoughts on what would be better?