The strap should be your last problem, as it's very easy to ask to JLC some other combo, and they will happily set the problem for you...
I totally agree with you, a black strap , or even a subtile grey, will perfectly fit your watch.
About the caliber 877, it is reliable and very accurate...I own several 8 days JLC movements, in a Panerai 198, or in the Reverso 70eme, or in the MMR ( 15 days PR) and no problems at all.
I'll try to post some pics, but I have to find them before! LOL
Best...And don't forget to post pics, as the Master 8 days is bomb!
Nicolas