The bleeders dissipate a bit over 0.5 watts. At full rating, inside a tube amp, they will get VERY hot! For reliability, they should be rated for at least three times the actual dissipation - you should use 2-watt resistors. A working voltage of 500v minimum is required, to survive the turn-on transient voltage. #things_they_don't_tell_you_in_the_specs
The different part numbers indicate how they are packaged, loose individual components, or taped together in reels of 4000 resistors for use in automated insertion machines. See the spec sheet, bottom of the first page.
