Yes, with the JA Pitts the firewall has to be notched, with the BME bango style no modifications are needed. Actually a simple job, on the cap x I assemble the firewall, on the extreme cap it is assembled and cut with a cutting wheel then box with 1/8" ply. All of the strenght is above the area to be cut, so nothig lost exept a little weight. One of the few small differences between the two is that the firewall needs to asembled on the cap x, just in case you would like to shorten it for some engines. With the BME I am able to use the supplied Hyde mounts with no firewall shortning or standoffs, just have to redrill the engine mount holes for inverted engine mounting! BUT BE CAREFULL, the mounts are slightly offset! Here is a pic of the Cap x, BME 50 JA Pitts. Extreme cap will be the same setup but with BME 44.