Thanks for all the responses guys.
Yeah I did consider the bulkhead spacing idea, but unfortunately the gap isn't parallel to the spinner either (it's about a perfect 1/8" on top, and down to 1/16" or a little less on the bottom) so even if it could be done it wouldn't get things perfect. Since on the firewall side everything is already perfectly aligned, cut, and drilled, I'm probably going to have to take some material off the front face of the cowl, reinforcing as necessary from behind as suggested by a few.
Now y'all have me worried about the 1/8" gap not being enough though! Anyone out there build to the spec 1/8" gap and have problems to the point where they wish they had made it bigger? Frankly, I'm not really as concerned about show-quality tight gaps or anything like that... if it looks ok, flies the same, and is just as safe I can see the justification for widening it up a bit. That said, I've already built it now with a tight gap, and it will be less work to make it an even 1/8" all the way around vs. taking additional material off.
As an aside, I've also aligned the cowl to be about 1/8" low to account for eventual engine sag. I'm hoping this is a good number to go with, as it too is pretty well set in stone (well, fiberglass...) and would be pretty difficult to alter at this time.
Mike Jimenez & Sarah Hammonds
EAA Chapter 33 Prez & Soc Chair
Marion, IA USA
RV-10 In progress! (N165MJ reserved)
-Emp & Wings complete
-Panel wired up, working on Fuse & Finish
-Blog horribly outdated (sorry)
-Fingers crossed for 2017 flight!