Some folks asked me about part swaps on these Reaper models back on this thread
http://leadadventureforum.com/index.php?topic=87328.0 so I took a stab at doing some lightly customized versions. These are the standard Bones-material Bathalian Exarch, Primarch, and Centurions with the heads and arms switched around between the bodies and repositioned for more variety.
Triad Alpha, uses the Exarch head and arms on each of the three different bodies
Triad Beta, uses the Primarch head and arms
Triad Delta, uses the Centurion head and arms
You could also swap the arms around and use them in different pairings (although the not-Tyranid scything talons arms probably look best when paired unless you're really into fiddler crabs) and with different heads, so there's a pretty tremendous number of potential combinations. You will need to do some cutting to make things fit on inappropriate bodies since the parts are cast "keyed" to fit, but Bones material is very soft and easy to work with. Doing these using the metal models would be a royal pain and cost about four-five times as much on top of the extra work.
Added 5/1/16, an experiment with asymmetry - big old psyker Primarch with a pair of "Fiddler Crab" bodyguards, with some minor body re-posing using the boil-and-freeze technique:
More effective conversion than I expected, and the unbalanced look is less obtrusive than I expected. Then again, I always liked the uneven look of the Roman retiarius gladiators, so maybe I'm biased.