Focus the heat on the knuckle and not the bolt. Once heated, quench it with penetrating spray like PB Blaster until it stops burning off. This will cause the parts to move away from each other and encourage the penetrating oil to get sucked into the spaced between them. If that doesn't work right away, leave it until the next day and try it again. It will work. It has to.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission