Please see my post in 2014 (below) which details how I did this.

https://www.talkmorgan.com/ubbthreads.php/topics/239758/mods-to-my-m3w#Post239758

The gauge I used was an SPA gauge which is digital and shows not only oil pressure but also oil temperature. This was purchased from Merlin Motor Sport (at Castle Coombe) together with the billet adaptor plate and also the extension tube that allows you to mount the oil filter with the billet adaptor plate in position.

I found this gauge to be very useful and very reassuring to know the oil pressure and temperature in real time. I believe there are a few other members that have also done this mod following my initial installation.
Good luck with it and a very positive addition to the car.

Keith.