Welcome! Glad you've quit creeping.
On the EFI head and compression ratio, you might want to read this thread:
300 Six Compression Ratio, Intakes, Heads, etc. And particularly, don't miss
this post.
From what I've read it seems like the bottom line is that you can increase the MPG on the 300 with the right single barrel Carter YF or YFA carb, good distributor advance curve, and an overdrive transmission. But, increasing power usually doesn't improve MPG - with the exceptions of raising compression ratio and/or going EFI.
Anyway, glad you are here.
Gary, AKA "Gary fellow":
Profile
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