Sounds like he's doing a "run stand" - I plan to do the same thing myself.
You will need:
The engine (duh! :doh: )
The control electronics
"A" radiator (you don't need the OEM radiator, but you do need something)
"A" fan of some sort (either the OEM fans, or an industrial air mover as a 'push fan')
A fuel source - you don't need the OEM fuel tank, but using the OEM pump wouldn't hurt - especially with the later HO engines (internal fuel pressure regulator.)
A battery (you could do it with a AC/DC power supply, but you'll end up using too much electricity that way.)
The bellhousing (helps to get the starter mounted up properly, and gives you a place to mount the CPS without fab work.)
Flywheel or flexplate (I'd prefer a flywheel for that, but either one will work. Make sure it's compatible with your control setup - HO wants and HO setup, not a RENIX.)
You'll also need to fab up a cradle to mount to the engine mount pads, a regular work stand won't do. When you get that laid out, I'd appreciate a copy of your drawing - I need to do something similar myself (I need to stomp up a couple of run stands for some experiments.)
Essentially, you'll need the engine - and everything attached to it - from the transmission end of the bellhousing forward. You don't need the transmission proper to do this, but the bellhousing will save you LOTS of fabrication work! Any bellhousing will serve - I didn't see where you are, but I've got a spare Peugeot bell around here somewhere, I'm fairly sure. The CPS and starter mount is the same on all transmissions.