Wee bit confused, but will press on... the goose neck is normally the boom fitting to the mast for the main sail (not the jib). If it's this then EEEEEEEEEEEEEEEEEEEEEEEEEeekkkkk
don't even think of using Al rivits. Think when you let the sail out on a run or a reach. The sail is basically supported at three points: the head at the top of the mast, the clew at the outboard end of the boom and the tack at the boom mast fitting. All three of these places take 'huge' loadings as the force is transfered from the sail into the boat structure.
On a reach the centre of effort of the sail is ~ 0.6 m aft of the mast, say the sail is ~14m^2 in a wind speed of 16 knots, with (dry) air density of 1.3 kg/m^3 this gives a force on the sail of: 328 kg ~ 1/3 metric tonne (in actual fact owing to the angle of the sail and forward speed this force will be slightly different to this, downhaul, main sheet tension and mast rotation ratchet up the forces). Taking a simplified case the lever arm acting on the goose neck is the force x distance at which the force is applied... which roughly is 200 kg of force ~440 lbs. This is napkin engineering, but it's trying to illustrate that a considerable percentage of the force is transfered to the boat through the goose neck fitting.
All boat specific rivits that I know of, in Europe are Montal rivits, which are okay between al and stainless steel fittings. Make sure you put gaffer tape or an insulating layer between the mast and the fitting before riviting.