Tank and filler kit

[Jdbfish]

Got a reproduction tank kit for my 68 swb c10. Box says its for a 69 to72 blazer. When I put it between the frame rails with the filler neck on drivers side, the neck looks like it will be right in line with the bed crossmember after the bed is installed. If I turn it around, the filler looks like it will be to far forward and come out under the pass side wheel well. The neck also will not quite clear the frame. What can I do?
Also, I would like to mount a gas cap in the bed floor, side of the stake hole, or behind a light. What is the bet combo for this? Pics pls!!!
I know this has been discussed many times. I did a search and found lots of info, enough to really confuse me!!!! Please help.....
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