I’d like to use carburetor mounting studs that are about 1/2 inch longer—how do I remove the old studs? Any recommendations on where to get new studs?
Thanks in advance.

To remove the carb studs, usually they will turn out if you clinch the stud in a Channel Wrench style tool. If they won’t twist out. Autozone and other car parts shops have a tool loaner program and will have a stud remover tool.
For a longer carb stud, I have used slant six manifold studs.

And here is a link with info on a source for the studs

http://www.slantsix.org/forum/viewtopic.php?t=48622

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Doo Ron Ron and the Duke of Earl are friends of mine.....
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I usually soak the stud with penetrating solvent (blaster, kroil, etc) then double nut the stud and turn it out.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

When removing sticky/rusty/otherwise troublesome fasteners, I always remember the 4 F's: Force, Finesse, Fire, F&!% it.

Force: Apply a reasonable amount of force. For a stud, that's gonna involve double-nutting or channel locks/vice grips. When that inevitably doesn't work, try...

Finesse: Penetrating oil. Clean off any rust or grease first with a wire brush. Oil liberally, tap it with a mallet, and let it sit. In some cases you might try tightening a bit to break it loose before loosening. (If you haven't acquired a stud puller yet, now's probably the time.)

Fire: Heat that sucker up with a torch. Try not to start a grease fire with all that penetrating oil you used.

F&!% It: Nothing worked, and you've broken or otherwise garbooned the fastener. At this point you can try your luck with a left-hand drill bit and/or an extractor. You may need to grind the broken stud flat, and you definitely want to use a center punch to start the drill bit. When that inevitably fails, drill it all the way out and tap the hole for a helicoil. If it's already been helicoiled, break out the wallet and use a time-sert. (Be very careful with the alignment, especially for a stud. The last time I did this I had to install a new mounting stud into a cylinder head after the manifolds were already in place. This may not be an option for a carb stud.) Also, try not to put metal shavings into your engine; by now you're already having a bad enough day.

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Somehow I ended up owning three 1964 slant six A-bodies. I race one of them.
Escape Velocity Racing

Thanks to all for the help. I was able to use the double-nut method and fortunately it took very little force!