which engine

i am going to be aquiring a 83 - 86 chevy half ton 4x4 pickup. it has a 6 inch lift and has 35/12.50/15 tires.
i was wondering which motor i should go with it has a 1970 350 with alum
intake and headers in it and i have a 400 engine ready to rebuild in the grage that one is a 76 i was wondering which would give me more power. i know there was a power drop off in the 70's somewhere either one i use has to be rebuilt.
and any other relatively cheap mods i could do to either to invcrease power.
thanks for your advice.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file

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.