Please don't kill me...

OK, here's my thought and apologies to purists:
Made my '64 Dart a daily driver with a rebuilt /6. It wasnt the original motor (numbers indicate '67 or later), but what was in it when I bought it. This particular car was rode hard and put away wet, used, abused, and generally mistreated. So I think my Karma is good for saving it and keeping it on the road. Everything under the hood is now new or rebuilt. Front discs, new interior, etc. outside looks like ****- but I live in Oakland, CA- its supposed to look bad.
But what I'd really like is a modern, fuel injected motor, more than 3 speed auto, more than 16 mpg, more than just barely 100 HP, and more than the 85 MPH top speed I get.
What motor/ trans combo could I put into it to improve daily 40 mile roundtrip commute (in traffic) mpg, modern reliability, hopefully better acceleration and speed, carefree 300 mile roadtrios, etc.?
I want to keep this car on the road everyday, but need modern reliability. Also, w/o that assurance the wife may make me give it up for a Toyota Camry or some such abomination- so please help me save my soul and keep this work of art rolling.