Here's your basic common or garden Advance Space Crusade Tyranid Warrior last seen on ebay with an upside down 'old-skool' Deathspitter and two rending claws. As you can see they've been removed, along with the top of his head. It's a painless procedure if you wedge it in a piece of blue-tac and shave pits off. Well painless until you absent-mindedly stab your thumb [but I mentioned that already].
Then you need a current Tyranid Warrior head, which is cool because each Tyranid Warrior box-set comes with two heads per body. Now I sliced the lower part of the head off but I've since seen another tutorial that slices the front of the old warriors face off and uses the New Warrior parts instead. Anyway this bit's tricky because it's harder to balance the head in the blue-tac without causing damage to yourself, so be careful!
First picture below is the side on view of the head glued in place. Then next up is some new bits added on. A couple of Monstrous Creature spines [although there's one of these, without the nicks in the chitin, on the Warrior Sprue. Also an Adrenal Gland on his front, bulks him out a little on the mid-riff.
Toxin Sacs were added to his head. The one on the left is a double MC one but they're all the same on the sprue so would have been upside down on the right side of the head, so I used two Termagant Toxin Sacs. On my first Prime I used only one Termagant Toxin Sac on each side. Game play you can run them as the toxin, or say they are Enhanced Synapse to raise your Warriors BS and WS. Really they're only there to mask the join between old and new head! You can also see a Termagant spike attached to the back of the head, this is also to mask the join.
Last shot is going to be the Lash Whip. This Prime is going to be armed with a Deathspitter [up top] and Lash Whip and Bonesword down below. Our current Prime is always footslogging with the other Warriors and having all out combat is useless. Having a Deathspitter will add an extra 3 shots, which have been quite effective to date, more so than his assault results. Alternatively a Devourer could have been an option to help lower Leadership but I'd rather go with firepower over the chance of a morale check...
Anyway, a donor Devourer had it's muzzle cut off and a paper clip was bent for the Whip. Don't worry about mounting it, drilling a hole isn't necessary, hold the wire over a candle with some pliers for a bit and it can be pushed straight into the handle. A bit of care and common sense with naked flames and scalding metal but it bonds real quick.
Next step, adding the arms and armaments...