the thing about spacers is they can add power, if you get the right one for your engine. i have seen 4 hole spacers add high rpm power, and i have seen open spacers add low end power. how much? about 3-5hp at best on most engines. like bnickle said use a 1/2" thick phenolic spacer to insulate the carb from the intake.
You can get a 1/2" spacer like the ones from Summit to fit for sure. I'm not sure about an inch one. When I was running a Stealth (which is slightly lower than the RPM), I could use a 1" spacer under the hood of my 66, but had to cut a little off the air cleaner stud and use a flat wing-nut. Currently my Torker 289 has a 1"spacer, too, but I had to use a 1/2" drop bracket for my RMP motor mounts to clear the hood.
Spacers are used as a tuning aid and can bump up or down the useable range. I normally think of 4 hole spacers as for improving the low end and open spacers as for the top end. The reason is that the 4 hole increases air velocity through the venturis and improves carburetor signal and airflow direction (most carburetor's throttle plates aim the air towards the back of the engine, so even a small extension below the plates helps to straighten out flow. The open spacer helps in upper RPMS by increasing plenum volume, by allowing a more gentle curve for the air flow to follow into the ports and by increasing the sharing of all 4 barrels for the whole engine (the RPM already has a cutout at the top of the divider for this purpose, so you just add to this). Different camshafts and carburetor/head/exhaust combos can change the engine dynamics quite a bit, so what works (open vs 4 hole and 1/2" vs 1" vs 2") for one engine may have quite a different effect on another. That's why what I just said is different (but often just as true) from what was stated by previous posters.
Spacers are a cheap and easy to install tuning aid (~$30 at Summit), so you can play around with a few and see what each does... Just clay the air cleaner (or use wadded aluminum foil) to see if you have clearance before you shut the hood.