What penetrating oil are you dosing it with?
Time, with it sitting so it's holding the penetrating oil, and let it sit.
Before heat ,strip it down, and heat and a quench, heat and quench, can cause the corrosion to get broken down. Doesn't work every time.
The carb is tilted. Any time water gets in , and sits, see how it is..

Anything you can do Safely,to make it easier for a machinist, will save you money. I cleaned up and removed the snap ring from an Explorer rear hub. First, the nearest nice mechanic. Blew the seals on his press. He fixed it, tried again, decided no to, sent me to a machine shop. Twenty bucks,, pressed out, New bearing in, snap ring, ready to go.
Attitude is everything.

Calling, asking, versus walking in with it, I usually just walk in, and I get treated great.
And one chance really is all you get, and IF you start and decide you'd rather pay someone, but you've got an off center, angled hole started,the machinist is in worse shape and you'll spend more.
At minimum, if I didn't have a drill press, I wouldn't try it.