Core support/Gas Tank Question

[Zukowner]

I am currently restoring a 1969 c10. I have purchased a core support for it, and I have decided I want to go with the grill from a 67-68. Is this going to be an issue with mounting or am I ok using the 69-70 core support with the 67-68 grill?

Also Rear Mount gas tank from LMC. I notice a lot of people have used the kits but it doesn't come with everything needed. I'm a little confused as to where to find a filler neck and how that gets located in the bed of the truck. I have seen them in the first panel of the wood floor, I have seen them in the middle, what do I need to make this happen?

Chuck.