Hi All

Thanks everyone for your replies.

rhenning - yup, definitely Italian thread & a 70mm shell. Doesn't appear to have been re-threaded, but I suppose that is definitely possible.

scooper - my bad. To badly paraphrase an excellent movie - my legs are tired, my eyes are old and bent.... Yes, you are correct. Dimensions should read - steerer tube = 25.4mm, seat post 25.8mm.

Has me baffled.

I was hoping the stamped numbers/letters on the drop outs would help ID the builder, but so far I've found nothing to narrow the field.