Helo Amigo, im pretty sure u can do the bosses right now.
Ofcours, u have to understand something easy - More lvl ,easier, and faster. I would recomend 350+/400 for make it confortable and not sufering.
Anyway for add more information, bosses like Hellgorak will never been defeated Solo, for kill this boss u need to use 5 convince creature rune (atleast) for make damage on boss, and u need minimum 3 ppl for kill this boss.
I hope i helped u