I am preparing a 351w block with 289 ported heads.
Now I have to connect the water-passages block to head, for what is needed to drill holes.
My question is,where you prefer to drill that holes, in the head or in the block ???
Because your heads have more holes for coolant than the 351 deck has. Those small little steam holes drilled in the 351 deck will keep any strange cooling system problems from happening with those 289 heads. Some times steam pockets form from not having those little holes in the block to match the heads. Sometimes problems do occur so better to do it and eliminate the possibility for troubles.
Don't forget to drill the headbolt holes for the larger 1/2" 351W head bolts.
I had to do this when converting my 68' 302 block to 1/2" 351W headbolts. The ARP bolts were a bit too tight in the holes when a 1/2" drill bit was used. I ordered a 33/64", and it worked. A more common 17/32" bit would probably work just fine as well.