How to make a boss health bar (17w45a-18w03b)

Here's the command (I won't explain what I, R, and C means from now on, go check the older videos (homing missile for example)):
1I: /scoreboard objectives add boss_hpbar dummy
2I: /summon pig ~ -50 ~ {Invulnerable:1,NoAI:1,Tags:["boss_hpride"],Passengers:[{id:wither,Tags:["boss_hp"],CustomName:"1+1=2",Silent:1,Invulnerable:1}]}
3I: /summon blaze ~ ~1 ~ {Health:100,Attributes:[{Name:"generic.maxHealth",Base:5}],Tags:["boss_ftw"],NoAI:1}

1R: /execute store result score @e[tag=boss_hp,limit=1] boss_hpbar run data get entity @e[tag=boss_ftw,limit=1] Health 300
2C: /execute store result score @e[tag=boss_hpride,limit=1] boss_hpbar run data get entity @e[tag=boss_ftw,limit=1] Attributes[0].Base 1
3C: /execute store result entity @e[tag=boss_hp,limit=1] Health float 1 run scoreboard players operation @e[tag=boss_hp,limit=1] boss_hpbar /= @e[tag=boss_hpride,limit=1] boss_hpbar
4C: /execute unless entity @e[tag=boss_hp] run kill @e[tag=boss_hpride]

Notes:
1. The pig in 2I can be changed.
2. The blaze in 3I can be changed.
3. The entity in 3I is the boss the player needs to fight, it can be any hp.
4. Concepts explained in http://www.minecraftforum.net/forums/...
5. Potato is truth, don't doubt that.
6. 1+1=2