NOS carburetors. What issues to be aware of if any?

I've used a couple of my NOS Thermoquads. Put it on, get it running, watch it closely for fuel leaks, if none you should be good to go. Keep an eye on it for a little while. Many years ago I bought a Holley spreadbore and I didn't use it for several years. When I installed it, it did not run very well, a small spider had got inside and made a home. I cleaned it out and it worked fine.