I seems it always happens when someone talks of using oem iron heads, the problem is the costs for valves, springs and machine work. You can spend two thirds the cost or more on a set of fifty year old heads that make 75 to 120 hp less than new a aluminum pair. This is especially true for the small Ford.
If you use stock heads you will need more cam and more rear gear to make the little 289 go.
Back in the day, right before all the aftermarket heads came out, I did a MAX port job on a set of 289 heads... and they flowed 218 cfm on the intake, and 175 cfm on the exhaust. This was GOOD for a set of 289 heads, and I had HOURS and HOURS and HOURS just in the grinding. Stock, the intake port is only 126cc, has a terrible design, and doesn't flow worth crap. The exhaust is even worse. My finished 'huge' intake ports measured 155cc.
Machine work and parts required:
New valve seals
New guide plates
New screw-in rocker studs
New Valve guides
Possibly new exhaust seats
Clean and magneflux
Machine for new, larger valves (bowls will be way undersized for the larger valves, and will need ported to take advantage of the new valves)
Competition valve job
Machine for double springs
Machine for pc valve seals
Machine for guide plates
Machine for screw in studs
Install and hone new valve guides
Assemble heads, and set valve spring height using shims
The above is just what I can remember off the top of my head... will cost nearly as much, if not more than a set of aftermarket heads, and will make FAR less power. Plus, you're at the mercy of local machine shops that vary WILDLY in quality of work.
Stepping up to a NAME BRAND aftermarket head with the correct valve springs already installed is a 'no brainer' move. Just avoid the off brand Chinese stuff, as a lot of that stuff is complete CRAP.