...I think you are probably not going to run into Raleigh proprietary threading in a bike from 1979, but you don't really give enough information to rule it out completely.
AFAIK, they were still churning out product with older Raleigh standards at the gigantic Nottingham factory right on up into the 80's.

If you just measure the width of the BB shell, and it comes out at a standard 68, you're good to go with a Shimano sealed unit replacement in the right spindle length. It gets considerable more complicated with the proprietary threaded ones.

Probably not an issue for you, but I thought you might want to rule it out, before you get too much farther into it.