Kinda late on this topic, but still wanted to share my thoughts on Koo Gum with Bie as the possible p'ek.
For me, if Exact were to pick an actor from their newer generation as the p'ek, Son would definitely have the perfect look of a Japanase soldier. But like many have already pointed out, his acting is still quite stiff and personally, it'd be awkward for me to watch him in those romantic scenes since he's not that good at showing his emotions yet; therefore, I would have to say I choose Bie over Son.
True, Bie might not have the look of a Japanese soldier, but acting-wise, I believe he could pull off the attitude of a loving and caring guy. Plus, if the author wants Bie as the p'ek, there HAS to be something he/she sees in him that fits the personality of their character.
As for the n'ek, I guess Vill kinda has the look and fiestyness, but again, it'd be awkward for me to watch her since I see her more in comedy/modern lakorns. And not only that, she's already got LOADS of lakorns lined up for her, so please give a chance to your other new actresses, Exact. :/
As for Best, if no one else has noticed, ever since KLKS with Mos, she's only been playing supporting characters in all her dramas. Her look, along with her acting, isn't that great. I mean, sure, she's one of the few actresses who doesn't need a lot of makeup to look pretty, but her look's just too modern and not right for this older type of lakorn. And honestly, I could never imagine anyone back then looking like her.
I think if we were to talk about acting skills, Aerin would be best for this role out of all of Exact's newcomers. The only problem is 1) she's not that pretty (only rarely is she), and 2) her voice kinda annoys me.
All in all, I would prefer Peung Kanya as the n'ek. Considering she's already been in two period lakorns and has the perfect and dramatic look for it, I think with a little more training, she would be great for this role.
Again, I'm only saying if Exact were to choose from their newer generation, Bie and Peung would be the best choices. Now if they were to choose from their more experienced and older generation, that would be a whole different story...maybe Captain and Aom would be the best choices then.
