Replacing the dipstick

I think the guy who had my car before me bent the dipstick tube so the headers would fit on. Problem is when i pulled it out to check the oil, it wouldn't go back in. I snagged a shorter dipstick from a tercel shopcar at my school (me teacher said it was fine) and then went to mopac to buy a flexible dipstick.
I was wondering if anyone has ever replaced a dipstick, specifically with a Lokar Flexible one. The instructions that came with it are pretty vague.
Any help would be appreciated.
And most importantly i guess, will i have to drain the oil to put the new dipstick in?

It's a 1985 pontiac grand prix with the 305.