We could discuss this further but the 1965 series production L8's proposed to 'fill-the-gap' were going to use Belgian 'Cannons' barrels who couldn't supply the quantity or the quality. Canadacould - and did but by then, India had told the UK
Government, in as many words '....... No Sterlings, No 7.62mm No4's either........'
The what were called 'spanner' barrels (with two flats) were a simplified barrel that could be fitted without the need for the more complicated part of the breeching up set. The drawings exist for .303" 'spanner' barrels with breeching up washers too............