I started rebuilding another bike

I am currently rebuilding a Fuji S10-S, a road bike from the 1970s. This bike belonged to my dad and is in very good condition. I watched it get rebuilt a couple different times over the course of my childhood, but have never ridden it. I'm posting about it to basically start a timer on myself. This bike is in very good condition and doesn't need much fixing, but the quill stem is seized into the fork and I'm unable to service that part of the bike.This is actually my first time extracting an extremely seized bike part, and I'm not sure how i'm going to go about doing it. I suspect I might have to resort to a hacksaw, which I super don't want to do!! I spent most of today watching seized quill stem extraction videos. I then attacked it with penetrating oil and blasted it with a heat gun and let it cool three different times. Next step is probably taking it to the co-op to access stronger penetrating oil than the stuff I have here. I gotta say, I do like rebuilding bikes, but I've seen…