Fuselage datum line 2+2/Pa-14

I am having some problems establishing the datum line needed to weld my fuselage top and bottom sections. Question: are the tubes that make up the firewall on a PA-14 (or PA12, PA18) set 90 degrees to the upper longeron (from the door post to the firewall)? The plans are a bit sketchy here.
Thanks,
Marty

90 degrees to the datum. In the case of your fuselage, 90 degrees to the upper longeron to sta. 2 , which is the sta. forward of the door post. I recommend working off the datum as the upper longeron while parallel to the datum in this area, they also narrow down to the 22.250 outside width at the firewall sta.Kevin

Thanks, Kevin. That is what I thought but I wasn't sure. I know this is critical in the fuselage fabrication and I want to get it right. I'll post some pictures on my site when I get the datum established, hopefully tonight.

Marty

www.xanga.com/martyfeehan