By " 27"sprint Rims" do you mean tubular/glued-on/sew-up tyres, or lightweight old British 27" x 1 1/4" tyre/tube rims?
Rims and tyres are best measured by the inside diameter of the tyre bead, or the outside diameter of the bead seat of the rim.
This is the ISO/ETRTO system:
(Ignore the 559mm measurement, that's mountainbike 26".)
700c rims are 622mm in diameter at the tyre bead seat, roughly the centreline of the braking surface, about 14mm smaller than the outside diameter of the whole rim.
This is the same size as all 27"/28" tubular tyre/glued-on/sew-up rims.
So, if you are just looking to change from older tubular tyre wheels to 700c tyres/tubes, you won't have to move the brake blocks, the rims are the same diameter.
If you have the old British 27" x 1 1/4" tyre/tube rims, they are a little bigger, at 630mm diameter at the bead seat.
So you'll have to move your blocks down by about 4mm to work with any modern 700c tubular tyre or tyre/tube rims. (630-622)/2=4mm
Hope that helps.
All the best,
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