Depending on how bad the surface finish is depends on how you prep.
I would steer clear of the Kero, use a good degreaser instead.
Begin with removing all the oil grease and rust.
Plug the barrel at both ends.
Check out how Larry Potterfield at Midway USA does it.
Gunsmithing - How to Polish a Rifle Barrel to Prepare It for Bluing - YouTube
Gunsmithing - How to Blue a Rifle Barrel Using Cold Blue Presented by Larry Potterfield of MidwayUSA - YouTube
I'd also polish the barrel and any other visible parts afer the 220 emery with 600 wet n dry then shine them up real nice with 0000 steel wool.
Also it is critically important to remove all traces of oil or grease from the steel surface, even the oil from a fingerprint will show in the finished product.
I'd also polish with 0000 steel wool between each application of Chemical Blue.
Finally the more layers of blue you apply the deeper the Blued finish will be.
I've reblued over a dozen rifles using this method.
The first one didn't turn out so good because I wasn't fussy enough with the prep, especially with making sure all the rust and oil/grease was removed.
Please Please Please DO NOT Reblue the Martini Henry.
It's way to nice to mess with the original finish.
Cheers
Pete
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