I have never worked on a 788 in .30-30 or .44 Magnum. All my experience has been with .222/3, .22-.250, .243, .308, etc. I have encountered both sizes of shroud thread diameters. It was my observation that a swept back handle and the smaller diameter went together.
As far as repairing detached bolt handles goes, I did one using a blank 110 Savage handle with the wrap around collar. Turned down the bolt collar, leaving a shoulder. Fitted the bolt handle, silver brazed it in place, cut the cocking cam. Seemed to be a more solid assembly than the having the stump of the handle induction brazed into its hole. Winchester made some M70 bolts with collared handles.