I made my own xmember for my 68 Charger, there is quite a bit of mods to the floor pan & torsion bar Xmember for the A518, I would not think that an A body would have more room.

1968 Charger COLD A/C Hilborn EFI
512ci 9.7 compression, Stealth heads, 4.10 gear A518 ODtrans 4100lb,10.93 full street car trim
2020 T/A 392 Stock 11.79 @ 114.5