Rebuild or Buy New?

[IntegratedTJ]

So just recently my father and I have started working on our old 1972 fleetside, long bed c10. We've got a 5.7l 350 sbc in it and we're stuck deciding between a rebuild or replacing rings/pistons or just scrapping the engine and getting a new one. Large amounts of white smoke come out of the exhaust upon startup up until it's relatively warm/operating temperature. Figured that this would be caused by worn rings or pistons or a blown head gasket or all of the above. The compression in the engine is bad. Compression tests also showed signs of worn rings (Starting around 70, jumping up to 120 after three tests. Compression is pretty spread throughout, up to 30 between each on the third test.) School is coming up soon and we'd like to figure out if this is worth rebuilding or even reasonable as far as cost, what we'd do to go about it, and if this block is even reusable. I can answer any questions and any help is greatly appreciated. (I'm 16, turning 17 in a couple days. Just now getting in to the craft, love it so far, just need a few pointers.) Thank you in advance.

Another thing: This truck had been sitting for 8-9 years before we fired it up a few weeks ago.

-Trever