When I designate the pocket I'm putting the 8-ball and I am successful and then follow it in with the cue ball - do I still win?
According to Wikipedia, a player will win if
The opposing player commits any foul, including scratching the cue ball into a pocket, or knocking it off the table, in the course of a shot that pockets the 8 ball
Therefore, you would lose because you scratch the cue ball into the pocket while pocketing the 8 ball.
In one shot pool, played with 2 1/4 inch balls on American type square pocketed pool table, the rule is: re-spot the black and incoming player has ball in hand that to say "put anywhere on the table" with one shot only.
When playing European/UK/Australia/South Africa "2 shot pool" on basically a mini snooker table with a rounded shape to the pockets, often times played with reds and yellow balls, the rule is: loss of game on any foul whilst potting the black ball.