I have been working on my SE as well. I was going to do the repaint and new decals, but decided not to. Any way, I researched out the typography on the decals as best I could. The best I found that would possibly have been correct was the "Frutiger" typeset for the SE and where it says "SPECIALIZED" on the Allez decal. It's a humanist typeset from the 70's and is very costly, so I opted out of purchasing it. It's a narrow version and it measured at 42 points for the height. Other fonts that will work but aren't period correct are:

Humanist
Swiss 721
Helvetica (modified a little)
helvetica Neue

You might be able to take it to a graphic place and see if they might be able to make one.