My 97 F350 parts truck I believe has original spark plugs in it and they've rusted pretty good. So goon in fact that two of them have been blown out...

Is there a tap I can use to clean out the thread holes?

Should I just bite the bullet and get new (reman) heads?

The truck has 115k or so on it and looks like it was used as a fleet plow truck. Although, it's not anywhere near as rusty as my 90 Bronco plow truck was... My 90 Bronco looked like it did time on the deck of the titanic...

 

Well the real question is, how much work are you willing to do without pulling the heads off.
Fixing the spark plugs is a time consuming chore. Depending on how they "blew out" depends on how long of a fix. I've snapped the hex off 6 spark plugs (one come out and one I didn't bother because of space) and it took about 6 hours to fix it all.
If the hex is still there, you can heat up with torch and jam a stick candle at the threads. Sounds dumb but it works better than any penetrating fluid. Reheat and reapply candle every time it gets cool enough to touch. Do this to all the spark plugs, not just the broken ones. You'll need all the help you can get.
If the hex is not there but part of the threads is, you need to make sure that piston is down in the bore, so that it doesn't get torched. Find a big ezout that fits the hole. You'll need to push the ground electrode out of the way when you insert the ezout, but then its fine. After 4-5 heat cycles of torch and wax, then heat one more time and try to remove the spark plug threads. Tap the ezout into the hole with a hammer and then I use a ratchet while hitting the back of it to help seat the ezout without stripping the grooves you just pressed into the hole.

I reccomend removing the inner fenders and everything to help gain access. It really helps.

 

Hex's blew out...

The engine's coming out of the truck to be swapped, so access isn't a problem and I agree, looking at it, if I had to do it in the truck the inner fender would be the first thing I took out.

Starting to lean towards pulling the heads...

 

Pulling heads is always easiest.
Look around for a set of spare heads. I found a BRAND NEW set of the later heads for 350$. Unused.
Once heads are off you'll get the broken plugs out. No problem.
You can also buy a spark plug thread chaser to clean out the rust and crap after. Never hurts.

I am an autolite copper plug person.... Except in my 460s. They usually get the cheap Bosch platinum plugs because they are the cheapest stainless sparkplug you can buy. I've had the autolites rust in and break off within a year, even with using copper or silver neverseize. May want to try those as well.

 

I'm going to ask about a set of heads at my local machine shop.

Any particular ones I should look for for an EFI 460?

 

I think its the F3 heads. Whatever the casting number on your 97 heads is the better head. There's only 2 to choose from anyway.

 

I know this is an old thread but I was wondering what the outcome was on your problem? I blew a plug in my 460 and the plug rusted off with no threads left. I took one out that was next to it and it looked as bad as the one that blew out. I haven't done anything else except stare and wonder. The truck has 110k miles and this is the second set of plugs and they are autolite I think. They have been in there about 5-6 years. I'm thinking those plugs are crap even tho they were platinum.