1st post here but cut me some slack I've been around metal working, machine shops and the like my entire life. The rust must be neutralized or eliminated as it will continue to progress and eat the metal. I agree with removing the existing cable guides after the paint has been removed. My choice would be to use glass beads in lieu of sand, it will be easier to control and the equipment is a little more user friendly. Check in your area with Engine Machine shops, as they generally have a blasting cabinet that will easily accomodate a frame and its related components. Then appraise the condition of the cable guides after they are void of paint. If warranted, remove them and have replacements brazed on by qualified individual. Possibly use clamp on type or get real trick and run the cable within the top tube. For my $$ powdercoating is not as bright and does not have the appearance of good automotive paint. Here is a tip... find an Auto Body supply shop nearby, they have more colors than you can shake a stick at. They will be able to recommend someone that does small jobs, used car lots also have guys that come around to fix door dings scratches etc on location, they could do this job in your driveway while you watch and after curing the paint is hard and durable, unlike that of a spray can, because it hardens and cures chemically which the EPA loves. I have a Paramount I had done this way MANY years ago and it has held up very well.