logandiana: Some time ago someone on the forum presented a spreadsheet summarizing the range of observed measured sizes for each of the "standard" bolt head numbers. The range within each is large and there is overlap. Your ideal solution is to find a Lee Enfield specialist with a drawer full of bolt heads from which he could probably find a suitable replacement for you. It's not practical to buy a couple of bolt heads hoping for a fit. As to whether or not you should do anything to try to induce your replacement to fit I'll leave it to the expert armourers to comment.

Ridolpho