I was sorting out some stuff the other day and found a bolthead that I had counterbored for .223. I'll never use it, you are welcome to it. Send a PM with your mailing address.
A barrel option is to use a take-off. Compare the breech dimensions of a No. 4 with those of most sporting rifle barrels, and you will see that many can be adapted. These usually sell for C$100 or less. If you want original appearance, only "varmint" type barrels will be long enough to finish at No. 4 length. A section of salvaged No. 4 barrel can be sleeved onto a shorter barrel. This will allow an issue front sight unit to be installed. When the barrel shank is machined, remember to bring the barrel back a bit toward the boltface. You don't need the gap where the .303 rim fitted.