There were several different castings for B21/23/230 heads.
The 160 was the one used on nearly all B21s. It has holes in the head for the K-Jet injectors. The 405 was used mostly on B23s, with K-Jet injection, but a few were made with blank bosses for use with LH-Jet (injectors in the intake manifold.) The 405 has a slightly larger combustion chamber and 'swan-neck' ports that flow better than the 160, 398, or 530. The 398 was used on B23s, mostly with LH-Jet, and had the same port style and combustion chamber size as the 160 head. The 530 was the standard head for the B230, similar to the 398 (LH-Jet.) The 531 was the best Volvo made, swan-neck ports and a larger combustion chamber like the 405, and a slightly more central spark plug location, and LH-Jet compatible. There is also a bizarrre head with no combustion chambers. I know nothing about this one...
Turbo heads also had sodium-cooled valves.
The best you'll find in the U.S. is a 530. We never got a 405 or 531-equipped Volvo here. Canada got some 405s. 531 is Europe-only.
There is an article on Turbobricks with some more specifics.
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