Nice to meet you, everyone (first post)

So after a couple finishes in the top 10% of my AG at some half ironman events, I've decided to upgrade from my 15 year old, 24 pound Trek 1000 with clip on aero bars and am going to purchase a TT bike. I've seen a fitter and my ideal bike would have a stack and reach of about 543mm and 411mm, respectively. One of the bikes I'm looking at (and have found super cheap) is a 2009 specialized transition. A large transition has a stack/reach of 526/405. Would I be able to make this work? The reach is almost dead on but the stack is a little low. Could 20mm of spacers solve my problem or would that reduce the effectiveness of the fit?

Thank you