A repair like that I would just grab a length of stock fire up the belt sander or bench grinder and put flat on that looked about right. Test fit it in the hole if it looked good saw it off to length and start on the next one.
If the angle is off a few degrees it is not going to make any difference.
The stock may well have been hot rolled but it was likly ordered pickled. A short dip in hydrochloric or sulfuric acid and the scale is gone.