You will normally be fine w/ hardened bolts and nylocs.

IMO I would use the shear pins or soft metal bolts. I know replacing shear pins can be hassle to replace and read where some even shear with ice chunk hits and stops the impeller, but the are there to prevent down stream damage.

roll pins are prolly used because they stay put and wont mess up the balance. Oh, and they are cheap and easy to install too. Why not just replace them with new?

I avoided roll pins because the second time around, they aren't always as tight as the original and because they are difficult to remove in the back. I did one snowblower with grade 8 bolts because roll pins are hardened too. This current job, I used two shear bolts and am hoping for the best. If they break, I'll use grade 8 bolts.

I'm no engineer, but since they are at the centerline of the shaft, I'm not worried about balance.