$00B8/$00B9 means P1/P2's weapon type. $05B8 means P1's first bullet's type. The value $04 means F. And $84 means F+R. After testing, both $04 and $84 are okay. But it won't happen if you charge the weapon.
$00FC is screen Y pos. The elevator is checked while $00FC=0 in common. If the player shoot something with F or F+R at that frame, the glitch will appear. But First elevator is different from the second one. I'm now making double player's run. And in my run, the glitch appears successfully at the next frame of $00FC becomes 0. And must let P1 do that, P2 failed.(I don't know the reason...) And shoot next enemy when $00FC becomes 0 at the second time. So if player can keep the F weapon and shoot something as soon as $00FC=0, the glitch will keep to the top, in theory. I'm not sure if enemy with HP=1 is feasible, though.