Sounds like you have a spider etc. nest in the burner flue. Check out these threads:
The big flame and propane smell is from incomplete combustion, due to the hot exhaust gases not having enough flue area available to go up as designed. Turn off the propane at the tanks for now, and turn off the electric to the heater.
You need to unscrew the screws holding the flue above the burner, which may be very rusty for an old unit. Carefully wiggle the flue out if possible and inspect it for debris/nests inside. Remove foreign objects and reinstall.
Not sure about your water heater of that vintage, but the burner etc. may be rusted and also part of the problem IMO, if incomplete combustion is happening.
If the above is beyond your skill set, please call an expert. If you remove nests/etc. from the flue, and the burner looks OK, your problem should be fixed right away. When you fire things up again, there should be no repeat of the problem. If there is, shut it down and turn the propane off at the tanks.
PS -- You need to check the entire flue for obstructions inside, and for blockages at the top of the tube. I am not familiar with your vintage heater. Any chance of posting photos of the layout?
PS2 -- You might also consider replacing the entire heater, as was advised in your old thread:
A 40-year old heater may be on its last legs, and very dangerous!