Cheers folks for the input.
I'd tend to agree with the comments about getting a sealed bearing arrangement sorted.
Think I have a cheap solution to the current problem though,just to get this lad back out again.
I've purchased the standard one piece BB(£6),which looks ultimately identical,and I'll lathe out the new bigger cones internal threads and tack it on as the adjustment is from the other side,and I can reuse that undamaged internal part along with the new bearings and cups.
Can anyone advise/direct me on going down the sealed bearing/new crank route,or possibly just transforming it into a one piece assembly. Will one piece require new pedals and sprocket?
Cheers
Colin J