~ I think it's QR848767. It was made 20th May 75. ~
QR848767 should be roughly a May 1977 casting, but if it was QR648767 that would be pretty much spot on for 20E5. **
** Note that this isn't an exact science so don't even think about dragging me into court to testify or anything!
Do you have any old rego papers for the vehicle it was in previously? Or a receipt from purchasing the engine? Surely you will need to prove you own it when going for registration? I wouldn't have spent cent one on it before confirming it wasn't stolen or whatever, do you have written confirmation from a police check of some sort?
Also don't try to over-stamp it, you'll only end up making it look worse. I guess if you want to fix it you could pull the heads off and have a machine shop mill just that pad the number is stamped on at a slight angle to the deck and then re-stamp the number (once it is confirmed that is).
Holden should have done this from the factory. I couldn't count how many times I've had blocks decked and lost the number, it's just a bad design that could've so easily been rectified.