The OC filter is for the Multigrade paper. The OA is for graded papers and not safe for MG. 6B is for X-ray material.
The bulb size depends on the distance from the work area. Might be 15w, might be 7.5w. When doing initial set-up, I do a quick and dirty to see if its close. Determine the base flash to give the paper a medium gray with normal development. Pre-flash the paper, then lay some coins on it for 5 - 10 minutes and process normally. Examine carefully after fixed. Any hint of coin outline indicates safelight fogging. When you think you have it, Kodak outlines a more scientific version of the test that will provide more comfort.
Safelight filters begin to lose their effectiveness with use and age so need to be tested periodically.
Bob