In the spirit of previous posts, that the keel is in excellent shape and should require minimal work & cost, let me offer this approach (which can be modified of course).
You don't seem to have major issues of rust like some of us have, but we also don't know what could be hidden under the existing paint. We also have to consider your plans for next year, sailing in salt water for extended periods... so we want to do it right and not have any lingering worries.
I would still recommend sand blasting the keel. This is the only way to be sure there is no hidden damage that will bite you in the butt later. Plus, you really can't underestimate how tedious it is to get cast iron really clean with sanding or wire brushes on a grinder. Its miserable and you will never really get it all out of the pores.
Sealing method 1 - use a gallon of Interlux Interprotect 2000. Immediately after sand blasting get the keel hung up and wash down with acetone then paint with multiple coats of Interprotect. If any minor fairing is required it can be done in between coats 1 and 2, you want to make sure you cover any fairing filler with several coats of barrier coat. The last coat allow to dry touch but still put a finger print in and apply your choice of anti-fouling paint. You shouldn't have to sand anything but the fairing filler in this process.
Sealing method 2, use only 1 quart of epoxy and the 1 quart kit of InterProtect 2000. Same as above, sand blast the keel and get it hung up asap and splash down with acetone. Get one coat of un-thickened epoxy on, let it kick off and get firm enough to be dry to the touch but still make a fingernail mark in. Apply any fairing filler required, hopefully not too much. Let Cure, sand to correct shape and then apply a second coat of un-thickened epoxy. Like the first coat, let kick off but not cure and apply a coat of Interprotect. You can get three coats of Interprotect on the keel with a 1/4 nap roller from a 1 quart kit. Remember the anti-foul paint has to go on right after the last coat is touch dry but still not cured.
With either method you must make sure you are using an epoxy based fairing filler, not polyester resin based. The easiest thing to do is just buy a can of powder fairing filler to add to epoxy rather than the additional cost of a premixed can of epoxy fairing filler.
If you buy a gallon of West Epoxy anyway to do other repairs with I would go with option 2 so you only need a 1 quart kit of Interprotect 2000. You would only need the gallon kit of Interprotect if you also plan to do a barrier coat on the hull as well. Being a previous fresh water boat you might not need this. Plan ahead!
You don't seem to have major issues of rust like some of us have, but we also don't know what could be hidden under the existing paint. We also have to consider your plans for next year, sailing in salt water for extended periods... so we want to do it right and not have any lingering worries.
I would still recommend sand blasting the keel. This is the only way to be sure there is no hidden damage that will bite you in the butt later. Plus, you really can't underestimate how tedious it is to get cast iron really clean with sanding or wire brushes on a grinder. Its miserable and you will never really get it all out of the pores.
Sealing method 1 - use a gallon of Interlux Interprotect 2000. Immediately after sand blasting get the keel hung up and wash down with acetone then paint with multiple coats of Interprotect. If any minor fairing is required it can be done in between coats 1 and 2, you want to make sure you cover any fairing filler with several coats of barrier coat. The last coat allow to dry touch but still put a finger print in and apply your choice of anti-fouling paint. You shouldn't have to sand anything but the fairing filler in this process.
Sealing method 2, use only 1 quart of epoxy and the 1 quart kit of InterProtect 2000. Same as above, sand blast the keel and get it hung up asap and splash down with acetone. Get one coat of un-thickened epoxy on, let it kick off and get firm enough to be dry to the touch but still make a fingernail mark in. Apply any fairing filler required, hopefully not too much. Let Cure, sand to correct shape and then apply a second coat of un-thickened epoxy. Like the first coat, let kick off but not cure and apply a coat of Interprotect. You can get three coats of Interprotect on the keel with a 1/4 nap roller from a 1 quart kit. Remember the anti-foul paint has to go on right after the last coat is touch dry but still not cured.
With either method you must make sure you are using an epoxy based fairing filler, not polyester resin based. The easiest thing to do is just buy a can of powder fairing filler to add to epoxy rather than the additional cost of a premixed can of epoxy fairing filler.
If you buy a gallon of West Epoxy anyway to do other repairs with I would go with option 2 so you only need a 1 quart kit of Interprotect 2000. You would only need the gallon kit of Interprotect if you also plan to do a barrier coat on the hull as well. Being a previous fresh water boat you might not need this. Plan ahead!