I've been unable to progress things much over the past few weeks, but today I was idly looking at websites about 118° vs 135° drill tips and learned something interesting...

The 135° tips seem to have been something of a 'Johnny come lately' and probably weren't well known when the 360 engines were first appearing. Therefore, I feel, the Chrysler instructions for drilling the holes is based on the ready availability of 118° drills and therefore that's the way to go.

I have located, by the way, all the items I need to make up a drilling jig. Necessity being the mother of invention, as usual. I have to have a minor operation next week, but by the end of the week I should be able to get to the Men's Shed and start machining parts to make that jig.