I've placed a set of DOHC heads side-by-side and compared them to SOHC heads..... same with DOHC/SOHC blocks. You'll find that the DOHC heads will bolt on, but there is a small cooling water passage between the exhaust valves on the DOHC heads that is fed from the DOHC block. The SOHC block does not provide the supply for that passage.

Frank

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum