Hi,
Welcome to HotRodders.com Glad to have you with us.
You have it bolted on the trans & ready to go,
leave the shifting rods hanging for a moment, you'll need a nail or something to put in the alignment hole, hold the shifting arms (what the rods are attached to) on the shifter so there lined up side by side & centered in it's housing, you'll see a hole in the center of the arms at the top slide the nail into the hole, now the arms shouldn't be able to move back & forth, now the trans needs to be in neutral, put the shifter levers that go on the trans on the trans with the holes at the bottom & leave the rods off, (their still hanging attached to the shifter right) now take one of the rods & see how it lines up with the hole on the leaver it belongs on on the trans & turn the rod in the direction it needs to go to line it up, counter clock wise to lengthen the rod, when it slides right in pin it & do the other two the same way, when you have finished remove the nail, now try it out, you want to make sure the gears engage completely, if they don't check the bolts with lock nuts on them on each end (throw adjustment), to see if that's what's stopping it, if not readjust the rods.
Good luck,
Rich