The S1 relay is still available from Ford!! It's also a technically better relay as the circuits never fail and it has a built in rev limiter (which does work), it's just 1 terminal that becomes dry jointed (cracked). The S2 relay can burn out tracks...

The S1 relay takes pulses from the distributor where as the S2 relay takes pulses from the coil.

If it had a quick blow fuse, then i'd fit a quick blow fuse back in...