Well, it's not really a 70s Series. Lots of folks use that term to refer to anything that is pre-80s Series.
With a Caspian frame, a Colt GI slide and a GI parts kit, it should be worth four to five hundred, in my opinion, even if it's just set up as a GI gun. I'd make the trade and take the minor financial hit - but then, I like 1911s and don't like Glocks.
As Shooter said, anyone can put a gun together. I'd check some things to make sure nobody went crazy with the files and stones.
Make sure the gun's empty.
Cock it, put the safety on, pull the trigger as hard as you can - see if the hammer falls. It shouldn't.
If the hammer stayed up, just take the safety off. D0n't touch the trigger. Sometimes actions are screwed with enough that the only thing that kept it from firing was the safety, and when the safety is taken off, the hammer falls. Make sure that don't happen.
Take it to full cock, keep your hand away from the grip safety and pull the trigger as hard as you can - see if the hammer falls. It shouldn't.
Lock the slide back, drop the slide using the slide stop - see if the hammer follows it. It shouldn't.
With the hammer down, holding it in firing position, take your off hand and pull the slide all the way to the rear (cocking the gun) and let it go WHILE HOLDING THE TRIGGER BACK LIKE YOU JUST FIRED IT. See if the hammer follows the slide forward. It shouldn't. Do this one three or four times.
Cock it, take the safety off, shake the gun around, slap it against your other hand hard - see if the shaking or the shock of hitting your hand makes the hammer fall. It shouldn't.
If it does any of that stuff - hand it back. All of these are signs of someone that did not know what he was doing, working on the action.
Take it ALMOST to full cock and let go the hammer - see if half-cock catches it. It should. If it does not - hand it back.
Lastly, dry-fire it, and see if you can live with the trigger.