I just tried the 6.0.8J from that link you listed, Mac128, and it failed on my PB170. I get the happy Mac, then a message in English that 6.0.8 isn't supported on my model of Mac. It's the exact same message I get if I try and boot a standard version of 6.0.8.

I can boot this version just fine in Mini vMac, which is emulating a Plus.

Too bad the links for 6.0.7J aren't working - I'd love to run 6.x on my 170!