DC-6/7 done up with CP-107 Argus and maybe some Neptune / Tracker ASW bits, as a precursor to USN P-3 Orion.
That would work well since both DC-6 and DC-7 are obviously structurally related to the
North Star (especially the radial CL-5).
If going with the DC-6, the airframe could just be a developed CL-5 - the RW CL-7 was a DC-6 analogue with 4 x P&W R-2800-CA15s. There was also a R-2800-CA15-powered CL-37 project in 1953 that was also derived from the CL-5.
I'm less sure about the 1952 CL-29. Engines were R-3350-85s (versus R-3350 TC981 EA-1s for the
Argus) but it is possible that the airframe was a CL-5 based DC-7 analogue.
A few design possibilities for your DC-6/DC-7 MPA analogue would be a belly 'canoe' fairing for payload (as proposed for the
Constellation-based Lockheed proposal for RCAF MPA) or ... a bit more radical ... the raised-and-glazed cockpit canopy of the earliest CL-28 proposal. The latter would give room for a large nose radome (or to keep an
Argus-style nose observer station.