quick question, I have to change the Temp sending unit on my 71, Do I have to drain some antifreeze first or can it be done without draining. Not sure how much will leak out.

Thanks!

Well, if it was me. WIth a "COLD" engine , I'd have the wire off, the old one loose enough to spin out with my fingers, the new one in the other hand, a drain pan under the engine, and do a QUICK swap. Leave the radiator cap ON, so it doesn't get any air. You'll loose a small amount of fluid, but not enough to warrant draining the system just to do a quick swap. If you have headers it might be a headache and wet sleeves. Rams horn exhaust manifolds should not be a problem.