If you did go with Helicils then M2.5 metric or #3-48UNC would be closest to the original screw diameter and pitch, As you say the very small whitworth threads would be hard to find a helicoil for so probably the only way to stay with 3/32" whit would be to drill out quite a bit larger and bond in some inserts with JBWeld made to fit with the 3/32" thread.