Most 6cyl HK Monaros or HK GTS's seem to be worth more with a V8 added as long as it is a Chev or LS1/2. Even a totally original Survivor GTS with its 186S and Opel replaced with a Chev and whatever box seem to not drop or even increase in value. In the end no-one wants to drive around with an Opel or a Powerglide, and Saginaws are almost non-existent behind 6cyl in Monaro or GTS.