I can help you there Pacific
my little boy was from a Rescue ( they got him from a breeder) we were told he was a Swiss.
But as he grew (and grew
) DD and I did some online guinea gazing.
Rex have coarse , short fur, little broad faces, low set ears, huge feet with big claws, curly belly fur and curly whiskers.
Teddy have a softer coat, straight belly hair and straight whiskers.
(USA guinea-pig sites can sometimes class Rex/Teddy as the same just to confuse )
Swiss have a 'halo' of soft fluffy fur, longer guard hairs and straight whiskers (and are higher maintenance so DD and I were relieved when GP3 showed his true Rex colours though we love him no matter what and we were prepared for him)
Purring can be a brisk brrrr in response to noise or when you stroke them.
Rumblestrutting is the whole body language thing- walking round with a stiff body, almost snakelike, doing a longer brrrrrrrrrr sound.
Popcorning is cute, they leap about, buck like a horse, leap, wheek. GP3 can do a funny little movement where he swings his bottom round turning 180 degress or leaps like a little frog 
Ours were in the run today then in their nice clean Pighouse with lots of fresh hay. Clean for oooh ten minutes