The only other way I know is solder them on. But with all the good scopes out there I don't comprehend why anyone would want to use iron sights on something like a .308 Winchester. If you just don't want to spend a lot of money on a scope, there are some cheaper options. I have a Nikon Prostaff 3-9x40 on my 30-06. It's a very clear scope for the money with 90% light transmission and a BDC Reticle I bought for $160. There's also a Redfield Revolution 3-9x40 you can buy cheaper than that I think. And if you want something more powerful the Redfield comes in a 4-12x40 for about $200 or $210 or so. IT's a very good scope for the money too with 92% light transmission. That's almost first rate. Anything much higher than that will cost you $300 on up. Also, I have seen Pentax scopes for sale at Academy for about $100-$120. They aren't a Leupold VX-3 by anymeans but they are functional, clear, and good enough quality they won't fall apart under heavy recoil. There are just too many scope options out there today. And the chances of a scope going Wonkers on you now days is much less than even 20 years ago.
Otherwise I would just have it drilled and tapped for the sights. It's not like you're going to devalue it, I mean there aren't but a couple million Ruger 77s out there today. And the cost of drilling and tapping is not much, maybe $20.
