Just thought I'd post some before/after pics of a product I used to remove the rust on my block prior to painting. Actually, the block had already been painted yellow, but I wanted to change to gray, so chemically stripped all the old paint off, after which I found the block underneath was rusty. The rust remover I use is amazing stuff as it's non-toxic and non-caustic and it's even fine to get on your skin and wont damage paint, chrome, plastics, etc. Anyway, take a look...
All you do is brush it on, let it sit for a few hours (or overnight), then rinse/wipe it off.
The product I used is called Deox Gel and is available from Bilt Hamber in the UK (where I live). I'm sure you guys probably have an equivalent product over there.