Unfortunately, usually rattling motor noise when you’re accelerating is a sign of detonation (bad for the motor), a few of the common causes of detonation (but not limited to) are too much total ignition timing, low octane gas, too much compression for the gas available.
Prolonged detonation can cause serious engine problems, piston and ring damage is one, which leads to severe blowby, such as you describe.
IMHO, I would check timing and compression. Occasionally, denonation can cause blowby and backing the timing down eliminate it, if too much damage has not occurred. A compression test will give you an idea if there is any damage in the cylinders.