The background states that the Chaos ships are older Imperial designs, and that during the early history of the Marine fleets they essentially used whichever designs were available, modifying them and improving them as they saw fit. This is certainly supported by the pre-heresy artwork, which pictures Marine fleet assets looking much like standard Imperial fleet designs with their armoured prows(see
here,
here and
here for examples) or more rarely resembling Chaos designs (see
here and
here) and certainly nothing like the current Marine vessels. Of course, M36 is not M31, but certainly some of the older vessels are likely to have still been in use.
One idea could be to simply use a slightly de-chaosified Chaos Cruiser model, painted as a Dark Angels vessel. Another idea might be to convert a hybrid design such as the Vengeance class grand cruiser (which is part of a selection of designs available to both Chaos and Imperial fleets, representing much older Imperial designs) or simply use the Vengeance model itself (although it isn'n the best looking ship to be fair.)

But certainly combining Chaos prows (or sterns - this example
this ship seems to have a Chaos style rear with Imperial style hull and prow) or other details with Imperial hulls, or vice-versa, could produce a more archaic looking ship design that would look good.