The source of the tapping/knocking has been found.

To put it simply the entire engine is FUBARED I replaced the cam and followers which stopped the loud tapping but then let us hear a slight knocking.
Took the sump off and got the shells off:



****ed.

also found the cam has been reground before because these are -25mm. so it'll need a new cam and possibly a big end bearing.

this engine has well and truely had it. god knows what else is wrong with it hidden.

time to find a replacement bottom end