avaiability of Petter m head studs

[magneto man]

Anyone know of a possible source of head studs for an M type appletop engine, also big end bolts?
A further question:- the head bolts protrude into the cooling water in the appletop and have brass nuts, but obviously in the case of the engine we are rebuilding the water has damaged the studs, as the top of the brass nuts is open! Is there normally some sealing plug or similar, fitting into the top of the nut to prevent such corrosion?

Thank you in anticipation

MM