84 Chevy half ton overheat

I just bought a 84 chevy half ton 305 3 speed auto, 350 tranny with 76xxx on it. Drove it 70 miles the first day then the second day after a few miles i noticed the temp guage was at 160 and a mile later in the red. I pulled over and watched as the needle buried itself. There was collant that had sprayed out of the resavore. There was no pressure in either radiator hoses. As it cooled both hoses sucked in on themselves. I let the cap off a bit and the hoses went back to normal but the cap was definately shot and had stopleak gunk in the spring part of it. The radiator was almost empty.
After towing it i elevated the front end and ran water through the radiator and it was cycling fine, just had up and down surge with the cap removed. I put a different cap on and drove it another 15 miles and it stayed under 210. It does have white smoke when starting it but seems to go away, aslo there is no bubbling in the resoivor,can feel bubbling in the top hose-to the thermostat when you shut the engine off.
Any ideas what might have happend and what i should check.