Tell me more about this Holden 308. From the way it sounds the only small cube engine us yanks had to play with that might compare would be a 69/70 Ford Boss 302 or Chevy's DZ 302.
they were and are still a great engine,for the cost of a full rebuild though a lot of guys are just fitting an injected crate engine of some sort,the 308s get stroked to 355 and 383,the later 304 destroked versions had good injection which gets used on these strokers also any carb like holleys,,the stock carb was the good ole boy qjet on the 308s which i like and the 253 got the stromberg ww2 two barrel,the later smog 253 got the qjet though,the first 253/308s only had pcv valves,the later ones got smog #$%* like egr and thermo controlled advance and shift points in the autos and all that horrible stuff with the detuned cam shafts,,the 253 and 308 shared the same heads and valves!there was a factory hotter version called the "L34"on 308s only that had slightly bigger valves and cam,,i have the L34 valves in mine,the early heads have no heat cross over,the later smog ones do and the stock alloy inlet manifolds warp,you can swap the later injected 304 heads onto the earlier blocks so long as you use the later injected type cam as the valves are staggered differently,those heads can be used with carbs ok,they are a good cheap head compared to having an earlier one ported or such and offer even better porting possibilities,do you want me to ship an engine over to you?