i got a 86 chevy with a 350 and a 700r4

i tow at about 65 mph at 2000 rpm with a 5000# trailer

the truck has 200,000 miles on it so i want to rebuild the motor
and i have a new trans for it

on a motor rebuild what cam and pistons and stuff would be best

dished or flat top

what intake i got a new 600 cfm carb for it

i get 10 mpg towing i would like to get better if i could

Ditch the 350 and build a motor more suited for your intended use.

454 might cost more now, but you'll be far happier in the long run.
Your milage will be just as good or better, cause you won't be asking as much of the motor.

Or at least build a 383 out of your 350. You'll enjoy the torque. Plenty of decent kits out there just look around. If you want to keep your small block. Or do as suggested and go big block.