I´m almost finishing an Akromaster ( .60 size french kit that looks like an Extra, but has some degree of dihedral). I installed on it an OS .61 FSR, which is and old model but has not been used. The problem is that the plane is out of the center of gravity because the nose is heavy. Any sugestions about adding weight to the tail or is it better to leave it alone

If you just leave it alone, it won't fly right. How nose heavy is it? If it is too nose heavy, you won't be able to flare, not enough elevator authority. Makes for interesting landings, like a spear. Add lead to the tail. You can drill a hole and glue it securely in place in the tail, or cut some covering and add it securely back there. Make sure it doesn't float around. The ballance has to be between the marks on the plans or it will not fly right and could crash. If your lead shifts in flight, that is bad too.

if a little nose heavy no problem, lot of nose heavy big problem,can run out of up elevator then will not fly.Can add weight at the bottom end of plane on the surface,drill hole in weigh then screw weigh to plane,make a door at the back of the plane and move battery to rear of plane ,or again,drill hole in weigh and door and bolt weigh to inside of door or hatch,even with stick on weigh I drill the weigh then screw or bolt to plane,seen to many problems when weigh shifted or fell off plane.
Have a goodun,John.