Mark,
The blocks are original to the rifle. I've been in touch with various Ruger guys on different forums and prior to 1976, the 1v in .300 WM came with "target Style" blocks, to be used with target scopes such as Unertl, Lyman or Redfield 3200. My rifle is a 1975. The later ones came with the same blocks but had 2 extra holes, 3.5" from the rear block to mount a "modern" scope. I've been advised not to modify this firearm as it is quite desireable & collectable. I'm told around 200 made possibly, no more than 300. I would like to play with this thing, if I don't sell it. My options are limited: Have a front block installed, as the regular Ruger rail won't fit, or buy a target scope, likely a 3200, and go shooting!
Mike