Good point...didn't think about safety issue; being a cheapass, I was just thought to save some resistors for other projects
The 500R is nestled pretty tight in against the pot and 5K, so 1K is easier to replace/mod with. Will work out what needs to get lower floor (~200R or so?).
I'll run it at 0.75V bias; the heat was ok, just warm, not hot. Though, my heat sink is smaller than yours, so may be keep it low (will test it out and decide). Yours is so beautiful, mine is so bland and ugly! So jelly...