I'd start with finding every available manifold, sort by price and review. Setting goals is nice, but you'll probably find you only have 2 or 3 choices to begin with.
You already have the injectors, 42# is a good number. They're not too big that you can't get a good idle... that's all that's really important (other than cost). I hope they were flow matched.
Get measurements of your engine bay area and determine if bottom or top mount will suite you more, then go from there.