I just went to tharsdax's web site where I bought my engine, and on there parts dept. page two they have three different type head gaskets. One gasket comes with a 47mm bore with holes for 8mm studs (it doesn't say for a F80) a second one for a 44 & 46mm bore that says it fits a F60 and a F65 motor with 6mm studs and a third for there F50 (the one I ordered) says it fits a motor with a 36mm & 42 mm bore with 6mm studs. So I should be able to narrow it down to one of three by checking my stud size, without taking it apart. If it has the larger size studs (8mm) then it has to be a F80. THATSDAX sells a F50 (47cc) a F60 (62cc) and a F80 (70cc) Lucky for me I no my engine manufactuer. Freewheeling frank you said you have both model engine's a 49 and a 80, are the studs for the heads the same size?