i was just wondering how i would go about replacing my conrod bearings and main bearings.
would it be possible just by removing the oil sump and doing it from underneath?
Assuming the crank is OK, yep but awkward. Conrod bearings are easy, one at a time. With mains, again one at a time, the trick is to use a split pin inserted into (each) oil hole to rotate the block side of the bearings into place using the crank. It's up to you whether or not you check the clearances; Plastigage is the only way that I know of to do that without pulling the crank.
Some soldar instead of Plastigage also does the trick.
How does solder tell you what size the clearances are?? Plastigauge comes with measurements on the package so you can compare them and see what size the clearances are.....How do you do that with solder?? If you cant get plastigauge, you shouldn't be building an engine!