Will it work? Specs are very close it looks like. I found a place selling a sail and they say the measurements on the one they have are 26' 6" Luff, 7' 11" Foot, 26' 2" Leech so maybe it was modified for a G-Cat 5.0? It looks just like the main in the G-Cat 5.7 identification section with the window up front and the same clew plate. Different colors though.

Looking at the assembly manual looks like it should be possible to run a 5.7 main on a 5.0 without the boom. Any thoughts?