The article I have from the Amer Rifleman, uses a ball, the trigger is cut and the sear is ground(machined) for vertical clearance, then a hole is drilled and tapped in the trigger guard to adjust sear engagement..the ones we are in the process(Slow) of doing now, we welded a plate on the trigger, and will drill and tap for sear engagement, then drill and tap where the sear spring is for overtravel...I have a tube of coil springs form Brownell's and will try to adjust the trigger pull weight by lightening the sear spring
I am not sure any of this will work on an Arisaka trigger, they cannot be uncocked by pulling the trigger and letting the bolt handle down
attached is the PDF of the article and the trigger in process