I've recently done a rb25 stand alone engine wiring converstion retaining the original
Rb loom.
It's very straight forward once you get into it slight differances depending on if you use
A series 1 or 2 engine also if you use a forward facing plenaum you will need to lengthen
Wires to afm and oxy sensor ideally with shielded wire.
Glad to help if I can pm me