I'll second Hotrod Lincoln's comments on Kroil. According to many test, (and my decades long observations) it's the Best rust busting penetrating oil. If I suspect a fastener is going to be a problem and time is on my side, I'll give it a shot of Kroil once a day for as many days as possible. This has prevented snapping countless bolts and screws, saving time and frustration.
If Kroil is not available, a passable substitute is a 50/50 mixture of acetone and automatic transmission fluid.
Good Luck on a great looking project!
RonR