Ralph,

I've been in the hobby some 40 years and way back, two glow plugs was done occasionally, my recall was that of an English made Irvine. Far too long ago, don't remember how well that worked or if there was a differing heat range strategy.

It's worth a try but how would you install two glow plugs into a conversion?

But your having mentioned it now has got me thinking of making yet another head for my Tanaka conversion. If that comes to pass and it works as you describe, I'll be sure to post the results. Neat.