I think TT is trying to say nothing is going to bolt on and make the bike run right without some work.
Some will cost more than others, but ultimately any carb change will cost way more than tuning/cleaning the stocks.
The cb500 will fit yours, same carb bodies, just different jetting and such.
I read something yesterday...believe it was funjimmy, made cr26's fit his cb550. You'll have to search though...I think he had an adapter made so they lined up. ANyway the cr's will cost 700+ alone plus the machine work and your own time.