If the return lines are leaking could be causing air to get into your fuel and that can cause many issues probably make it hard to time correctly but I'm not sure, the "power stroke rattle" is usually a sign of timing being too far advanced and the smoke when starting is likely caused by the air intrusion from the return lines leaking. Is defiantly fix the return lines/ o rings first the whole kit can Be got for 50 dollars or less and is fairly easy to do. Do this first and see what happens it may fix some of your problems if not at least you won't have leaking fuel anymore
Anything on the return side might make it hard to /start/, but once the engine is running, after 30 seconds or so, it doesn't matter at all... because it's on the PRESSURE side of the lift pump.
If you are getting air after those 30 seconds, you've got a leak pre-lift-pump. Which means rubber hose loop that goes to the lift pump(likely), OR the lines going back to the switchover valve, OR the switchover valve itself(unlikely I think), OR where the lines attach to the fuel tank, OR the fuel pickup(likely)