i used 8ga on my truck, alt b+ runs to the lug on the relay, then from there i feed into the cab bypassing the bulkhead (coz it was melted at the terminals). used 12ga fusible wire as well.
ordered one of the repro Denso style alternators, just looking for 60amp output, the test sheet shows the alt puts out 120amps at 13.5V...hope my 8ga wire is ok.