I've used Autolite 104's for stock to mild modded with no issues for past 10 years or so. Cheap and work well.
If going for MPG, i'd suggest a few simple mods and get the MPG up there pretty well. My old 98 GTP before I scrapped it was mostly a highway driver only,
and was getting around 500-550 miles on each fill up, and usually had 3 gallons left in it. Was high milage car.. I had converted it mostly back to stock. Still had a S1X CAM,
3.4" pully, and I left the top of the air box off, cause well... I couldn't find it. If i had gutted the cat, probably could have tuned a bit more to get a few mpg out of it. Tuning was key.
Ran it a bit on the leaner side of things and what not as I wasn't racing around in it. Took a few days of driving to work and back (100+ mile trip) and got the tune down pretty
good. The trans was old and slipping and drove it like that for 4 years. That probably caused a bit of a hit possibly.