154 is probably so called "big bore" horizontal and this with 52,4 mm bore (and 49,5 mm stroke) is probably marked as 152 FMI, not 153. This one is "small bore" horizontal and his displacement is 107 cc. Also, internal layout is, IMO, differs - the big one's clutch basket is probably on the gearshaft, while on the other engine, clutch basket is on the crankshaft. As Italians would say, "in breve": no parts swaps there.