If you have it bored .30 over, balanced rotating assembly, get new rod, main, cam bearings, full stainless roller rockers, good aluminum heads, edelbrock performer intake, get your quench at .40, get 10:1 compression, some headers with a full mandrel bent exhaust, a good hydraulic roller setup with less than .230 duration @ .050, a nice rebuild quadrajet, and most important get a GOOD TUNE, and use synthetic fluids in the trans, diff, and engine after break it I bet you will get some decent mileage.
Ok, What if I buy bolt-ons, and change all fluids to synthetic... Clean it up, seafoam it.
(Because I have no idea where to buy any of that stuff)
The only things I have researched are some Throttle bodys Cold air intakes Tuners and such for a new mustang. This is way different.
I may be the only one taking this side of the debate but I bought a GM 350HO Crate Engine, hooker supercomp headers with side pipes, then installed a Tremec TKO500 Five Speed, changing out the rear gears to 3.55, steeroids rack and pinion steering, rebuilt the front end, rebuilding the rear now. Depending upon how many miles you have on the car and how you want to drive it you can go as wild or as mild as your pocketbook can handle. I cannot wait to launch my new "77" next spring. I did a fair amount of research on the engines. You can get 290HP with a basic 350 Crate Engine as well, in the $1900 range. I went for 330HP. The ZZ4 is quite a bit more expensive, well above $4K I believe. Also, watch out for turn key, the serpentine belt system won't have clearance under your hood I have been told. I went for the deluxe, not the turn key, then added aluminum radiator and spall fans. Have fun with your build and good luck.
Here is a price list I have come up with for you
Hot tanking, freeze plugs Boring, honing, truing deck, new hyper .30 over pistons, cam bearings, balance rotating assembly, press on pins, labor and install should be about $850.00 This is assuming you assemble the bottom end yourself, which I always prefer to do anyway.
Arp Main Studs For 2 Bolt - 57.00
Double Roller Timing Chain Set - 28.00
Lunati 60100LK Voodoo Cam and Lifter Kit - 175.00
Patriot Fully Assembled Aluminum Heads - 895.00
Standard Volume Oil Pump - 35.00
Head Bolts - 50.00
Pushrods - 50.00
Stainless Full Roller Rocker Arms - 150.00
Tall Valve Covers - 50.00
Edelbrock Perfomer EPS - 125.00
Rebuilt q-jet - 150.00
Felpro Master Gasket Set - 54.00
Flowtech Headers - 160.00
New 2 1/4" exhaust system should run about 400.00 Total - $3206.00
This is of course if you have the cherry picker, and reuse a BUNCH of stuff from the current engine such as the distributor, timing chain cover, assuming motor mounts are still good, air cleaner, etc..... Plus all the buddies to help guide you through the rebuild.
But you would be shaving weight off the front end, plus you would be getting better power and wouldn't lose any driveablity with this.
If I lived near you I would be more than happy to help you. Anyway, good luck no matter which route you go.