If you need to save space with pulley mounting, about the only possibility is grub screws at the bottom of the V. "Grub screws suck" is a bot building truism but sometimes there are no alternatives. You can improve their reliability by grinding flats on the shaft, using Loktite on the threads and using the largest possible grub screw. Drilling a recess for the point of the grub screw is another option but harder to do with a silver steel shaft.

I am not sure about how your hub arrangement looks, but its really hard to put screw threads into Hardox. Its not totally impossible but will need a specialised tap, ultra-heavy cutting oil and a precisely sized hole. Most builders use an aluminium tube or block and tap into that. By coincidence Ellis just posted some inspiring examples:





You probably won't need quite as many bolts as Ellis used