I've seen dual exhausts with the spare and aux tank in place, so it can be done with factory manifolds. But long-tube headers move the starting point of the exhaust system back quite a ways, and that might make it difficult.
As for the heads, I don't think Ford had "fuel injection" heads for the 302. They did for the 460, and they were so different that the intakes and exhausts from a carb'd engine won't bolt up. But I hadn't heard that there were any FI heads for the 302/5.0L. Did I miss something?
Gary, AKA "Gary fellow":
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Dad's: '81 F150 Ranger XLT 4x4: Down for restomod: Full-roller "stroked 351M" w/Trick Flow heads & intake, EEC-V SEFI/E4OD/3.50 gears w/Kevlar clutches
Blue: 2015 F150 Platinum 4x4 SuperCrew wearing Blue Jeans & sporting a 3.5L EB & Max Tow
Big Blue: 1985 F250HD 4x4: 460/ZF5/3.55's, D60 w/Ox locker & 10.25 Sterling/Trutrac, Blue Top & Borgeson, & EEC-V MAF/SEFI