Boxerworks.com

Yep, allen bolts are the go - officially 'Cap Head Screws' in the catalogues.
3/4" unthreaded length sounds too much to me - better measure before you buy.
1/4" diam fitted perfectly, almost an interference fit. M6 bolts would be a tad loose. Don't forget to get an Allen Key that fits the head, if all your keys are metric.

The Allen bolts are referred to as Socket Head Cap Screws.
Guy

Just a thought here - I saved my old wheel cup and bolted a metal bar to it to make a tool to hold the final drive splines while tightening the drive input nut.

Used the "drive strapped to the wheel" method for removing the nut, but I think this'll work more elegantly, and it's free.

Good tip, Thanks!