Apocalypse Rules Question?

[Waaaghpower]

So, I have a question about how to interpret an Apocalypse rule, and then an adjustment of rules that I wanted an opinion on.
First off: The Tyranid Heirophant is listed as a 'Psyker' with the Warp Field Power... But Warp Field isn't a power anymore. In 4th Edition, when Apocalypse came out, the Warp Field power just gave a 2+ and a 5++. Now, there is the Warp Field *Upgrade* (Upgrade? Ability? I don't know what it is called, but it isn't a Psychic power anymore) but it is listed specifically as giving*Zoanthropes* a 3++.
Now, me and my friends were just going to interpret this as the 4th Edition rules and simply give the Heirophant a 5++, but I wanted to see what everyone else thought.

For the other thing: I wanted to use an Orkified version of the Necron Pylon. Should we just keep the rules as is and use an Orky model, (Which would mean I gain no benefit from the 5++ given to Necron models,) or change them so that it's more Orky. (IE, reduce BS to 3, replace the 5++ with a 5+ cover and/or obscured for vehicles, replace Living Metal with a power field.)
In the Apocalypse rulebook it says you can take models from any army you want, this is more of a fluffy 'Opinion' question.

[The Man They Call Jayne]

Don't know aboout the first, but as for the Pylon, I would make an Orky Pylon and keep the standard Pylon rules. Just find a fluffy way to justify it. It doesn't have living metal, it is filled with highly caffinated grots with tools reparing the damage as fast as it happens. That kinds thing.