I'm a motorcycle guy, (not HD, Imports)
As I don;t come from 'automotive' I don't have preconceived idea's about what is 'right'
454 is about 7.6 litres, 500bhp is about 65bhp/litre, not a particularly good output in my opinion, 85 is reasonable, 100 or more is good (around 150~175bhp/L is 'normal' for motorcycles I work on, even 1970's low rpm make about 90bhp/L at the wheel with stock cams and carbs)
I like small ports with thick walls, you can shape them where they need to be for best flow without being oversize and losing driveability
Personally, I would buy a cheap electric die grinder and router speed controller (Harbor Freight tools, probably less than $75?)
plus some GOOD carbide burrs(expensive, about $30.00 each) and open ports closer to 'stock' (even though rectangular ports are not so good for flow)
Do a bunch of reading/searching (articles by David Vizard are always good)
Stock BBC heads respond well to only minor clean up, I see no reason why the small port heads wouldn't do the same?
It all depends if you have more time or more money, quickest thing to do would be bolt on some decent heads, cheapest thing to do is DIY