Roadpaver

Can someone give me exact directions to correctly put the demi hoss buckskin parts on my avatar so my avatar can look like the demi hoss avatar it's suposed to when I have it on my avatar. I'm asking because I have no clue how to apply alphas without avatar's legs and chest disappearing every time I try. In other words I'm having trubble with setting up whole demi hoss avater to fit onto my avatar. Sorry if this sounds a little confusing. Note: the avatar is a mesh avatar.