New engine to my Chevy c10 1975

Regards, I am about to start rebuilding a Chevy c10 1975, in my country Ecuador is very difficult to find parts, but I plan to travel to USA to get everything.
I want to add new engine and transmission, I want something that is reliable, nothing extravagant, I do not need high power, better reliability and low cost, which would recommend ?. Beforehand thank you very much.

It may most economical to install a factory crate engine. Many of those are assembled in Mexico so freight costs may not be prohibitive. A new long block Gen I V-8 would bolt right in and accept the same accessories as the original 1975 parts.

Looking in some pages of the USA I found this http://en.chevrolet.com/performance/connect-cruise-powertrain-systems, but I do not know if it is the most convenient option, since I am looking for something to inject, I have thought to go to SEMA This year, what could I comment on?
Regarding the engines in Mexico, I find interesting but, do you know of any contact or distributor? Any information is very helpful.
Thank you

I definitely recommend a drivetrain that would have been common to that truck, and very reliable. 350 V-8, and either a Turbo-Hydramatic (TH) 350 automatic transmission, or a TH-400 if you plan to tow a trailer or haul heavy loads with it.
Preferably both of them would be fresh and rebuilt by some of the many companies that rebuild a lot of them here in the USA.