In general the firewall sections didn't have too much complication. Applying tank sealant to all the seams was a bit of a pain, but not particularly difficult after building the fuel tanks. The hardest part was probably getting the bends for the stainless steel sections at the tunnel entrance to align and lap correctly. Once attached together, the parts are very stiff and difficult to manipulate, and it actually required quite a lot of pushing and bending to get everything to align right. Once it all snapped in place the fit was actually pretty good, but the clecos were somewhat insufficient to hold it all together. I had to create a few shims with #30 holes to keep the clecos from pulling out on the curved section of the tunnel while setting rivets. Otherwise, the only modification was to leave out the exhaust brackets since I elected to use the EXP119 engine, and instead I just put blank rivets in the holes that would normally hold the steel brackets. I kept the doublers behind them, however, figuring they still provide some rigidity and structure.