I assume you mean viscous clutch fan, not thermo fan? Thermo fans are electric motors. Not sure how you got a 6cyl shroud around a V8 fan though. What I would do:

Fit a late long snout V8 pump and pulley to suit.
Use a 3 row (or more) radiator that is clean and not clogged up
Buy a factory V8 shroud off Greg.
Use a factory HQ-HZ viscous fan (not WB onwards as those square blade fans don't work with the earlier shrouds).
Makes sure there is a decent strap from the battery 0V/-ve terminal to the radiator support.
Run 2 x bottles of anti-corrosive additive (not green glycol as it goes all gluggy).
Use the right thermostat.

The above seems to keep Holden V8's nice and cool. With a manual 308 you can get away with a 3 row and a fixed 4 blade fan.