Option number 3 is your only choice for not permanently altering the rifle; which we would encourage you not to do. I have no experience with one, but it should work.
Another option is just to buy an Arisaka that someone has already scoped, it may not cost much more in the long run.
Welcome to the boards, but please don't drill and tap your Grandfathers's bring back Arisaka.
03man - Don Voigt
Author of "The Japanese T99 Arisaka Rifle" 2010 edition
Co-author of "The Knee Mortars of Japan 1921-1945" 2011 edition
Near Charlotte, NC