72 Blazer in need of advice

[DW56]

All

Bought my 1972 Blazer about a year ago. First 4 wheel truck I have owned. Complete opposite of my slammed 1956 Ford F-100 for sure. Enjoyed driving the Blazer the way it is shown in the pictures, but while recovering from some minor health issues, have decided to make something of this Blazer. I occasionally will use the 4 wheel drive (NP205), but not often. More than anything, I drive back and forth from the airport in it and the usual trips to the beach. Currently has a 350 carb'd motor with the TH350 trans. Motor runs fine and sounds great, but I may rebuild the motor as a summer project. Not getting double digit highway mileage out of it for sure. On the freeway at 65 miles and hour, I am usually at 3000rpm. If I could get double digit mileage and drive on the freeway at 70MPH while at 2500RPM, I would be happy. Again, total blast to drive. Really enjoy pulling up to some idiot in a Prius and blowing exhaust on them. Have plenty of them to choose from out here in Liberalville, CA

Looking for suggestions: Am thinking if I rebuild my current motor, and then change the trans to a 700r4 will the trans fit? Anyone using a gear vendors? Or, should I just change it all out for a used LSX motor/4L80E combo? What clearance problems am I going to run into if I change to the LSX/4L80E combo (have to assume the cross member for sure will have issues, but what about the transfer case)?

I have looked for links to my questions, but dont find the exact answers. I am sure they are here and that I am just missing them.

Thoughts? Suggestions?

Thanks
Dana