Slitting saw questions

[Toolmaker51]

Most slitting saws are narrow, they don't tax power of a milling machine. Slotting cutters require a degree of rigidity in spindle and part set-up, most certainly.
There is no assurance in threaded boring head arbors being concentric, or engineering concentricity into the connection of the cutter arbor.
I'd turn in one set up a cylindrical and on size fitting your largest collet and 7/8" or 1" for cutter. Then you'll need a keyway, cap, and socket head screw. Flat heads offer the most clearance, 1/4" is sufficient. Counterbore the cap deeper than the 7/8" or 1" 'spud' to accommodate narrow slitters, commonly .015. The key is best engaging cutter, arbor, and cap for obvious reasons, many over tighten this screw and deform cutter flatness. Put it on so cut is CW rotation and loosening will never be an issue.
Don't be disappointed in commercial or shopmade arbors producing uneven sound during the cut. Unlike boring [a single point operation] or milling [comparatively smaller diameter & proportionately greater space tooth to tooth]; slitting is particularly difficult to maintain the exact feed rate and chip load. Watched expert tool and cutter grinders sharpen those also; concentricity is not a question.