Technically, they aren't "freeze plugs". They are core plugs. The holes in the block are there in order to remove the sand from the casting process.
In my experiences, the coolant pressure doesn't pop the plug, the plugs corrode on the inside where you can't see it, then eventually fail.
The only way to be assured that they can't come out like that is to convert the block to screw in pipe plugs.
I did that on my 68 302 block. It has the added safety features plus it helps stiffen the block for high performance use.
The 69 and 70 Boss 302 blocks came with threaded pipe plugs installed. A few other Ford blocks intended for high performance use did also, but not many.
Some late 427 blocks. The C7FE GT40 block. The Boss 429 blocks all came equipped with them.
They are not difficult to install. You need a 1-1/2"NPT tap and the pipe plugs. Those taps are not expensive since they are commonly used by everyday plumbers.
Here are some pictures of the Boss 302 block v. the 68 302 4v block.
I installed a 347 kit in my original block. From the exterior it looks stock. You can't tell it's a 347. In addition to the plugs I also am using a main stud girdle.
I think that the threaded plugs are worth the effort and time to install.
Ford installed them for a reason for maximum durability under extreme conditions. Ignor that as you wish. It's your block.
It is more important to have threaded plugs in the oil passages as you can see here in the back of the block.
On some engine like the Q code 428's, they used press in plugs. Considering that you are running at least 50 psi cruising and maybe as much as 100 psi with a high volume pump, pressed in plugs NEED to be replaced with threaded inserts.
