The slant is longer than the 218/230.
You want a 225, which is a tall deck (10.68") engine (which is why the slant: hood clearance).
The 3 X 1 Australian engine isn't a slant 6 but (almost) a hemi, no parts interchange. Nice engine but I've never seen one.
The 225 block won't support as much power as it can develop, something less than 400 has been reported.
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Easiest: Eaton M90 from a GM 3.8 V6.