Angus242164;c-139448 wroteB230ET's definitely had 531 heads, I've owned three, the 531 was designed for and first used on this engine in '85.
Other sources are '93 240 with B230FX, and '93 onwards 940 with B230FB.
There is also a 531 head with K-Jet injector holes in existence, used on Volvo factory exchange reconditioned B23E's, I've owned two of these.
My understanding is that all 530 and 531 heads have the small coolant passages, as all were manufactured after the change to small passages in about '84.
you forgot to add your bibliography