My concern about using stuff like Evans is that a 3.9 Morgan in standard tune ought to have adequate (admittedly marginally so) cooling.

If it's overheating, then using a waterless coolant might be masking a problem (e.g. partially blocked radiator?) which doesn't strike me as a good idea.

Fitting an oil cooler and/or an enlarged alloy radiator seems to be a much better strategy.

Tim H.
1986 4/4 VVTi Sport, 2002 LR Defender, 2022 Mini Cooper SE