Strange engine blow-up Options

[Trackday-Dave]

Hi Guys
Hope I'm in the right place, got major prob's with 3 sge engine and I'm at a total loss as to how.
the story is oil level sender gave up the ghost, picked up a 3sge motor for £50 for spares, removed dead sender and relaced with good one. so I guess we lost about 2 lt oil, son topped up with 4.5 lt unknown to me,(so I guess we overfilled it) engine worked alright but on his way home through liverpool it started rattling it's head off, (he lives 40 mile away) managed to talk him through what I needed to know was under the rocker cover, lobes are perfect so is rest of top end (head)
any ideas as to what has gone I suspect bottom end but would overfilling cause such a problem,
really desperate for knowlegable input and thoughts

tony