You can get Tru-Turn spinners cut with 1.20 size slot in several sizes of spinner. Not custom order, but in stock, off the shelf. They fit the common 15x8 APC props nicely with no trimming. You can have them custom cut a spinner if they do not offer it off the shelf for most popular props (I do have one nylon GP spinner with aluminum back plate that I did have to cut the prop slots for, but most of my aluminums spinners did not need a thing).

I don't think the Dave Brown adapters have the double lock nuts. I'll take another look at their product line, though. I would not use a single nut adapter on a 4-stroke if there was a double lock nut type available, even it it did cost a few bucks more.

Pilgrim