They appear to have the same thread size and spacing, so the fit presumably should work. Did the CP-703 shotgun capsules screw directly to the CM700 preamplifier body and not either the 0dB or -15dB barrels?
One (potential) issue that may need to be considered is whether or not the shotgun capsules will be adequately powered with an “active” (chopped) setup. I seem to recall that the CP4 shotgun capsules did not work with the CM300 “active” setups. I had both active setups at one point, but only ever ran the CP4’s a couple of times on the actual preamplifier bodies.
So, to summarize, this post is of no real use at all.