I think it would be best to have all the timing marks lined up just in case something moves and so that you can see if anything has moved.
Once you line all the marks up, lock your belt to your cam gears and lock your cam gears together (so they can't rotate), depress and pin the tensioner, then you should be able to remove the tensioner, replace the pump, refit the tensioner and everything "SHOULD" still be lined up, but at least you will be able to turn it over by hand a few times and check to make sure before you fire it back up.
Have fun scraping the old paper gasket off the block, I know I did (NOT) :evil: .