Does the UK use the European octane rating system? 98 in Europe is like 93 here in the US. Though you did have lead in it, so it is not really our 93 octane no-lead.
Just trying to help the OP get calibrated on the octane requirements he is going to need with N20.
OP, note that Hot metal is running lower DCR than you with that .590" lift solid flat tappet cam. So you will start out a closer to detonation issues than he did.
