85 chevy Help

Currently I am in the process of rebuilding my 85 Chevrolet truck from top to bottom. I am seeking advice on my choice of engine and transmission combo. It currently is all original with a 305 and TH350.
When completed I will be driving it around a 100 miles a day, and I want an overdrive for better gas mileage. On the weekends I go to the lake and have a boat that weighs about 2500 lbs. What is the best combo? Can I get 20+ mpg and still pull my boat around locally?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Good luck getting 20mpg pulling anything.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sorry for the confusion, of course I meant without pulling anything getting 20 mpg and when I do pull something having the power to pull it available.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Newer Chevy truck 4.8 or 5.3 with associated transmission and computer from salvage yard should come close(closer than others) to doing what you request. Any year should suffice. HTH, s
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I would try the 305 with 700r4 and 3.42 rear axle ratio with highway tread tires. This is a pickup, isn't it (1/2 ton)? Do some research and find a cam with a good power range fitting for your driving plans based on tire size & final drive ratio. Make sure your carb is right. If needed rebuild it and pull the plugs covering the adjustments. Or use a older model quad. If you really serious about mileage, get and old model 2 barrel carb & re-jet it. This may take some trial and error, you want them small but not too small. Just needs to a be set right and have a light foot. It will be hard to get much over 20mpg but 20-22mpg would be my guess.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.