All that is needed for this achievement is to get all stat upgrades available in the Max tab on the pause menu. Facial appearance you will unlock progressively in rank I'm not sure if it's needed for this, everything other stat upgrade you will need to purchase with scrap.
Here's what is needed to max out stats:
Knuckleddusters for fist damage
Ammo belt(need to reach road warrior rank for last upgrade)
Head(I don't think this is needed because it's not listed on the stats sidebar, they will all unlock as you progress in rank)
Tools( same as head but I do suggest you upgrade this whole sidebar ASAP)
You do not need to Max out your Griffa abilities for this achievement.
Tip: If you are going for this and scrap collector it willl take more time if you are purchasing everything so I only upgraded Max abilities, skills, tools and ammo belt as needed then maxed out everything else when I got the scrap collector achievement.
If there is anything you feel I missed please comment.