In the order I would go about it; 1-change over to electronic ignition(pertronix ignitor's easier than going to Duraspark,either work well) 2-put on a 2bbl carb from a 2300 4cyl 3-header,or at least a good free flowing exhaust system 4-cam swap 5-the later(78-up I think)head is a bit better all around,performs well for the old integrated intake type head(log head) 6-255 v8 pistons-gives a bit more compression,supposedly a direct "drop in" 7-get the new FSPP aluminum head w/detached intake(pricey,about $1700-1900) the first three is about as far as I would go as far as throwing money at these sixes.Very durable,just not very fast unless you turbo or heavily modify(read-$$$)them.
gear swap would be a good one too the 6cyl stuff does get expensive. i never got too deep into mine since i knew my money would be better spent on a 302
if i was to swap it to a 302 what would the gas milage be like? and would i be able to just drop it in or would i need to modify suspension or steering?
you could probably maintain low 20's with a 302 as far as the swap its mostly drop in. suspension and steering is all the same. since mavericks had 302 you just need the factory mounts and related pieces and it'll be in its hard to talk about performance modifications to someone who's worried about mpg's tho. if thats the case a few I6 bolt ons are probably what you want
Go here: http://fordsix.com/forum/ I built a 200 inch 6 with about 175hp that was great. 262 Isky cam, 250 head with a Holley/weber 2 bbl carb from Stovebolt, header and a 5 spd... Lots of fun.
I spent about $1100. to do a complete rebuild, Isky 262 cam, lifters and V8 springs. New pistons, deck the block, new water pump. Mill, Port and message the head, new valves and rocker shaft. Add a 2bbl carb and adapter. I found the header at a pick a part for $20 and coated it for $100. The install was done by our Falcon club. We did a BBQ install party. My 16 year old son hooked everything up and got it running for me. I was recovering from surgery and couldn't do much back then. The guys got tired of seeing the parts all over the garage. A few weeks after we got the car running, my kid took it into auto shop and installed a T5. It was a great runner. Had more medical bills so it had to go last June.
As for the 302 mileage, if you build it to breathe, not necessarily to absolutely scream, you can get good performance as well. Performer or Performer RPM, Comp 270H, 9:1 compression, good headers, good dual exhaust, 600 CFM carb of your choice tuned properly, and most importantly, drive it like there's an egg under the accelerator. I got 24mpg highway out of my setup, stock 302, Performer 289 intake, 8:1 compression, Holley 600 vac sec, AOD and 3:1. Swapping to the Autolite got better city mileage, but I didn't really check for hard numbers. The AOD actually hurt in town as the converter was so tight it accelerated slower, took longer to get into drive. I actually got better on the highway than we do in my wife's 2000 Explorer.