the rb 30 is a nissan engine.
the dohc head costs 750 comes with inlet manifold, fuel rail etc.
the r32 rb25de head is a straight bolt on to the rb30e bottom end - no modification.
your turbo is fine (im using the rb20 one which is high flowed till i can afford the biggun)
rego, insurance, dont tell em
resale - prolly get more buyers
changing cars character - what, u like a lotta lag? stalling it to 3500 to take off at a decent speed?