GT40P question

From what I have read here on this forum the only thing that needs to be done to install a set of gt40p heads on a 351W is to drill the bolt hols to 1/2". I am installing a set of gt40p heads on my 83 sn2001 this week and the one question I haven't been able to find an answer to is;

Do you recommend drilling the head bolts out yourself or is this something that needs to be done at a machine shop or mechanic?

Thanks for the help?

Here's a picture. Basically the cutting edge is ground to a 0 degree rake. "dulled" See the flat on the cutting edge in the K picture.

Hi Josh

the first time I did this I had a short conversation with myself

It went like this

Me #1 I wonder what size drill bit I should use for this ? All over the internet people seem to say 1/2 inch

Other smarter me Why don't you measure the hole in the original 351 head?

Me #1 Why didn't I think of that?

Other smarter me That's a good question, just go do it

Me #1 OK I did it, the hole is 17/32 inch

Other smarter me Are you sure?

Me #1 Yep a 17/32 drill bit fits perfectly in the bolt hole

Other smarter me Good job

So take it from both versions of me, you'll need a 17/32 inch bit.

I figure Ford knew what they were doing when they made the heads and that's the hole size they made.

And like Pete said use a drill press. People have done it with a hand drill but the chances of drilling at an angle are a lot higher. If you drill at too much of an angle, you end up with a hole into the water jacket, then you have water in the oil. The casting isn't very thick where you're drilling.

Me #1 might know this from experience in case you're wondering

Also you'll need some new spark plugs. A good Autolite number is 764 or 104.

They're functionally the same plug but the 764's are half threaded and the 104's are full threads. If you look in the plug hole when you get the heads you'll see why either will work

Or you could cross reference to your favorite brand.

One Ken O or the other

Oh and by the way, me #1 ain't so smart and I just used a good 17/32 bit with no modifications , went slow with the press and it was no problem

The slower the drill press the better. 150 RPM or less is good. No coolant, just drill it dry.
Cast iron tends to glaze with oil. If the press is too fast then you can use straight water to cool the bit. Little tip: cut a small piece of cardboard and lay it over the existing hole. Crowd the drill bit gently into the cardboard. The cardboard tends to center the drill bit over the hole. Drill thru the cardboard. Obviously you need a new piece for every hole. It keeps the drill from grabbing and walking around till it finds center.
(.531 and 17/32 all the same when you are searching for the bit)

Well I'll tack on to this thread so as not to make another one. Who knows...maybe this could become the GT40P reference thread. I searched and found just a few threads and this seemed to be a good candidate to add to.

So say one has stumbled across a pair of used heads somewhere somehow.
What can one do in that moment to decide if they're worthwhile to take?
Can one reasonably see warpage?
Can one reasonably see cracks?
Can one reasonably see burnt valves, weak springs, bad seals?
Anything else to reasonably look for?
What might be the going rate on used heads?
Would one need to take them to a shop after deciding to take them and spend more money on real examinations and/or re-doing rockers/springs/seals/valves anyway?