Royal Sierra or Spirit of '76?

[Chan-man]

I will posting pictures in a couple hours and I'm wanting this post to gain some traction. I purchased this truck when I was 14 for $3,000 and now I'm 25. I'm trying to figure out the real info on this truck. What is it? Doing research over the years I've found info but very little and very vague. Looking at this truck it's a 1976 GMC Royal Sierra 1500 1/2 Ton Long Wheel base 2WD. One side has an emblem and the other doesn't. I do have a second emblem I purchased online. The weird part is on the inside it has blue door panels with an emblem that says "Spirit of '76". According to online the Royal Sierra model was made for 1976-1979 GMC models as a trim package and the Spirit of '76 model was for Chevy. I'm curious if someone has thrown something together or if this is an actual model that was purchased this way. Is there anyway to find additional details on this? Does anyone have extra knowledge on this particular type of truck?