Got this from another site.
I guess if you get the oil cooler adapter(the sandwich part) you can mount an oil pressure sending unit to it.

Oil COOLER
The oil cooler is fed off the "oil cooler adapter' which is sandwiched between the oil filter housing and the block. For a IIa, the feed line should arc over the engine (behind the water pump) to a junction on the inside of the LH wing. This is where the oil-temp capillary sender connects. After the cooler, oil returns directly to the sump (oil pan).

OIL PRESSURE
The Mechanical oil pressure line should attach to the oil filter housing. You will attach the oil pressure line between the oil pressure warning switch and the oil filter housing, using a banjo fitting. You do not need to disturb the oil cooler lines at all.

 

Wise Owl Innovations Incorporated - Land Rover Parts

This may be what you are thinking of...third item down.

 

Guys,

Check this one out. I would go with this type.
Oil Filter Sandwich Adapters

They have the adapters, guages, and everything needed for simple addition of good oil pressure/temp guages.

 

According to the site, the adapters come without any senders, gauges or wiring. Just pointing it out so no one buys one thinking it's a kit in a box.

 

Just to bring up this dead horse. I noticed that everyone that has done this left the adapter down at the OE location running a tee or whatever adapter there. I was wondering about having a small hydraulic hose from the mounting point for the sending unit to a more, uh, advantageous location...any thoughts?

 

Depending on how and where you mount it you might need to bleed it so it provides accurate readings but it should work. Just make sure you use a very good quality hose. A braided stainless line would be a good choice. If the hose breaks while you are driving you will roast the engine in no time.

 

I would point out that if plumbing allows, having both the oil switch and the gauge are a good idea. If the idiot light was wired to make an noise (and mute the radio) even better. SWMBO's as a group consider red lights (at intersections and on the dash board) as challenges to be overcome by pressing on regardless. I prefer the electric sender method, I've had an oil line to a gauge let go under the dash and it is messy. If going mechanical, there is a nylon hose for the pressure line that can be used instead of copper, it does not conduct engine noise into the cockpit as much.

 

i did this with the sandwhich adapter, which allows you maintain all the stock functions/sensors as-is


fits fine with the big filter as well



mechanical oil pressure gauges are a terrible idea (in my humble opinion of course...). just run electrical stuff off of a sender and never worry about lines fatiguing or rubbing through and causing a fire/dumping oil on your feet when it breaks loose in the dash.