I have NOT installed my outer cowl Woody but perhaps let me say what I found since you ask what to go by...the inner to outer or the outer piece.
I ordered a new inner to outer and a new outer cowl panel from the same vendor. Their inner to outer would NOT even match up to their own outer cowl panel...but, get this, MY OLD inner to outer panel fit their new outer cowl. So what this means, at least to me, is that their outer cowl panel is good but the inner to outer sucks!
I took my old inner to outer panel to a guy who replaced the "sides" of it that were rusted almost totally out and it looks good. I just have to figure out exactly where to drill the emergency brake hole! (all for $25)
Several post on this "inner to outer" panel took place about a year ago. I was actually posting the remarks sent back to me from the vendor and their promises to get with the "manufacturing folks" and see what was going on. Later I got an email that said "we been selling these for 15 years and had no problems". Well, I sent them copies of stovebolt letters telling how we had to beat them into submission to get them to work but I was almost accused of Vendor Bashing here and the thread stopped...all because I was telling the TRUTH and revealing a popular vendors attitude about it!
So, beat, heat, twist and hammer into submission. Its the best you gonna get. :mad: