New to engine swaps. Work will start soon

Im getting a 1979 J20 in about 9 months after deployment and the truck has been sitting in the mountains for only God knows how long. The engine started right up when we found it but i am feeling like I am going to need either a rebuild or swap. Its got the AMC 258 inline 6 and I'm thinking the AMC 360 might work. Anyone point me in the right direction so i can start purchasing parts so that when i get off deployment i can build this monster?!  

Thanks for your service!
A few questions:
What do you want to use the vehicle for?
What is the shape of the engine?
How many miles?
How maintained?
How technically adept are you?
The 258 is a pretty good low end torquey <sp?> motor
With a couple of fixes ( a Weber or if CA smog a Howell TBI EFI )can
be a real good engine.
A 4/0 head.
Nutter bypass.
Change all the fluids ( gas too ) do a compression check.
Then wheel it til it breaks.
Then fix.
IMNSHO
J.B.  

its going to be weekend fun run truck for sand mud and rock. the engine wasnt in too bad of shape but i dont think it will be running for very long. we cleaned her up very well flushed the coolant, the oil, and the fuel. i didnt get to do the compression check on it though. the maintenance... lets just say that my grandparents bought there house in '97 and they we doing some clearing of the land because we had some nasty fires up in the mountains recently and they found the truck. so im guessing that the maintenance hasnt been on schedule. im pretty good with cars and trucks. but the whole technical like numbers and ratios and stuff im not that good with. i can build it if i have the right guidance. thank you very much