What 351 heads fit or work on a 289 1968 ?

im pretty sure that you can run any sort of windsorhead that you would like as they are of the same engine family. though they run bigger valves, and flow better they also have much bigger chambers and thus a drop in compression and a lessoning of power and performance. youcould have your existing heads ported out for bigger valves and it would most likely cost less than the perchase and rebuild of a set of 351s. the only way to avoid the issue is to run a higher compression piston.
you could also go aluminum which usually flow quite well, dissipate heat more effectively, thus allowing for higher compression without the worry of pinging. but they deffinitly detracts from the classic look.
hope this helps some

Just taking a 351 head and putting it on a 289 will drop the compression ratio 18% from whatever it was on the 351. A 10:1 will become an 8.2:1 which is the ratio of 289 to 351.

If you decide to give it a try, (not a recommendation), you have to get special head bolts and intake gaskets for the 351W. The 351C heads can also be made to fit, (called a Clevor), but special intakes, machine work, etc. is necessary. The 351W heads, as already pointed out, have some drawbacks in performance as well as economy (The 289 will be a bit stodgy on the bottom end and will suck gas for sure). A properly set up 289 to run 351 heads is possible and is a real performer, but it is not economical or cheap.
Best,
Al