rcathey's instructions will work but I have a quicker answer. From a chart from Lyman showing the application of sight bases for various firearms,
they show a front base having a height of .475" from the top of the base to the center of the bottom of the base. The bases (called blocks by target shooters)
are listed as a Lyman O and Lyman E. Even though the scopes and mounting assembly are commonly referred to as "Unertl type", Lyman was using
them years before Unertl came on the scene. The chart shows the bases on 6" centers. To get 1/4 minute clicks on the sight they should
be mounted on 7.2" centers. The chart shows the same blocks for the 1903 NRA Sporter and the 1922 series (.22 cal) as for the issue
1903 even though the barrels of the Sporter and 1922 are slightly thicker than the issue 1903 barrel. I suppose the slight difference could
be dealt with a few more clicks of elevation. Setting all the detail aside, the quick answer to your question is .475" height for the block you need.
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