So where you running the 424 on a roller motor?
Again I think this is more to do with making the tunes safe for the average driver, the 304 can take a heap more timing down low, why is it my old VN V6 could light up the rear tyres easier than my HSV Senator? When I got my Senator the distributor was set at 12.5°BTDC (the poor mans tuning tool) on top of the HSV tune
Greenfoam proved the 304 can take a heap more timing down low without issue. If you compare a 165 to 185i tune, the majority of the fuelling changes are around peak power, down low the maps are fairly much identical.
Holden deliberately reduced throttle response on the 304 roller motors just like they did with the ecotec motors by putting that large lump of alloy inside the TB that keeps one side of the butterfly covered (and reduce the flow by half) until you get to about 10-15% throttle.