Tamid;
Just my personal opinion of course, but if those bbls are sound I would in no way consider destroying them to sleeve. I know its a matter of terminology, but you do I suppose realize that cutting off the forward portion of the bbls does not make their stubs into a "Monoblock". In order to be a monoblock the breech section has to be originally machined from a single piece of steel, thus "Mono" meaning 1.
Your intended use would of course determine the chokes needed. Unless you plan a lot of "Long Range" use for it a Cyl/Mod combination can be an extremely useful gun & would require only adding choke to one bbl.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra