4-bar / back half the HemiDenny / HDK way
I know from previous lowered Dart builds the lowest point is normally the bottom of the exhaust collector(s) @ around 4-1/2" to 5". If I'm above that by point by 3" to 3-1/2" ....I can live with it. I considered moving the trunk floor along with the fuel assembly higher, but with the bottom of the tank already higher than the 4 x 3 dipped in the center crossmember / lower driveshaft loop, I did not see the value of the increased effort.
I'm not a fan of fuel cells, especially located in the trunk of a street car. I like the design / function of a steel / OEM style tank installed outside any enclosed space with 20 ga sheet metal between any occupants and fuel. While the tank will fill from inside the trunk, the filler will utilize a sealed cap with nothing venting inside the trunk area.
Just the way I like to do things....others may vary.