Two different Pro Gloria heads on 7th ed soldier body, and a 6th ed. soldier body.
Same Pro Gloria heads.
Left: 6th edition warmachine crew legs, 7th edition goldsword torso.
Right: 7th edition general legs with 6th edition starter set captain's torso.
Body: Pro Gloria. Arm: 7th edition goldsword.
1st picture: Head from 6th edition soldier kit
2nd picture: Head from 7th edition archer kit
3rd picture: Head from 6th edition militia kit
4th picture: Another head from 7th edition archer kit
Verdict:Big beards, big hats, and big helmets make the head look larger than it actually is, regardless of manufacturer.
6th or 7th edition soldier body + bearded and helmeted Pro Gloria heads: go for it.
Pro Gloria body with certain beardless, hatless, smaller-looking GW heads: go for it, with precaution. (meaning
some 6th ed. soldier heads and some 7th edition archer heads)
Other combinations: Avoid.