you can put the o2 in one tube, some will disagree with that but just keep an eye on the spark plgs, My Holley HP efi only has 1 o2 on the left bank,

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