Classic/Antique Car Repair: 1973 Buick Apollo, buick apollo, exhaust gasket

Question
I am having some problems with my car. I am having some major problems with my car. I was driving to work one day and as I was giving it a lot of gas it backfired, the motor turned off and immediately came back on. it did this twice. I had my brother adjust my timing. It kept doing it, but only if i was accelerating up a hill or something. so I changed my fuel filter and put new spark plugs on it, I also put a treatment in my gas tank that would remove any water if it was in there. The car would still do it if i was giving it a lot of gas. I knew it was coming time for an oil change so this morning i check my oil and it is one quart low. which is not the lowest it has ever gone. I was driving to the auto parts to buy a filter and oil and the motor made a strange noise and then it started making a ticking nois, a loud ticking, not like an exhaust gasket, really loud, the motor rocks back and forth a little bit from the size of the cam so i though the header was banging on something but sure enough it was coming from the motor. I get my car home and I put it in the driveway and change my oil, I put a quart of Lucas in the oil following someone's advice that if a tap-in was stuck from the oil being low that thick Lucas treatment would relubricate it and get it moving correctly again. so I start my car and I have it running, it is still ticking, and after about 5 minutes or so, it makes another strange sound and then the motor starts to die. i try to start it and it doesn't want to start, it was as if it was trying to fire but couldn't really so i choked it and tried to start it again and it still wouldnt start. so i let it sit. then when i tried to start it again it was turning irregularly, my dad told me to take the dist. cap off and crank it to see if the dist. was turning and the dist. was turning. i put the cap back on, tried to start it and it made a very loud noise like metal hitting something. i tried to start it again a couple times and it does nothing but grind. it doesn't have the high pitched noise like when a starter grinds, it just grinds. and my dad looked into my radiator and it is completely empty. and it was not empty before all this happened. so my questions are... what do you think has happened? where do you think my antifreeze went? could it have drained somehow into the cylinders? because it is not anywhere I park. and finally do you think the motor can be rebuilt or will I have to get a new one? the motor is a chevy 350, small block, it has been bored 40 over, my cam has a little over a half-inch lift and my pistons are 220's if any of that would matter. the motor was rebuilt not long ago and prior to this all my problems with this car have been with ignition coils/plug wires and steering columns.I take great pride in doing the repairs myself but I have never had any motor problems. any advice or insight would be very much appreciated. Thank you for your time

Answer
Rebecca;;
HI- Well the first thing I would do is to pull the valve covers and check the rockers and push rods and springs, than I would do a compression test on every  clyd.  than I would check the cap-rotor-wires-points and cond. /  replace if bad. than I would pop the no#1 cyld. to check that the rotor is on the no#1 rotor spot   on the dist. cap. # 1 spot. when you pop it on.-t.d.c. this way you will know it is not the chain or off a tooth.  and check all vacume lines and p.c.v. valve. you might have a bad lifter / push rod/ or lifter. as far as the engine. if you were going to rebuild it- I would first look into a crate motor. a turn key engine. ready to go. you might save in the long run. a 350 or a 327  etc. if you do a web serch on (crate motors for chevy small v-8) you will find a lot of them