Has anyone converted a Triples Rule oil pressure gauge to a braided line
Ye-e-es-ish - not the TR gauge specifically but the similar, GB-available Wika used by Trevor Gleadall when he owned L.P. Williams, and a few LPW T160 kits.
Assuming you're talking about a twin, and you want to use Goodridge fittings:-
1. My Wika gauge is installed in the TR-type bracket that also mounts the speedo. and tacho. Trevor supplied the gauge with a brass fitting that turns the outlet through 135 degrees (i.e. from vertical to a bit below horizontal); otherwise, the hose would've had to go though the headlamp shell!
You don't say whether you have this bracket or the o.p. gauge only; if the latter, bear in mind that -03 (3/16" i.d.) braided hose must not be curved to less than a 1-1/2" radius.
2. On my T100, with the o.p. gauge mounted in the aforementioned 'three-clock' bracket, I used a little under 1 metre of hose - 0.96m or 0.97m iirc. This allowed enough slack for steering movement and that the hose must be curved to approach the engine o.p. switch hole from below - you can't do it from above because of the curve of the timing chest.
3. Only thing I don't know is the thread on the TR gauge. Trevor/LPW supplied the aforementioned brass fitting with 1/8"BSP male outlet thread so I used a Goodridge 321-03P 1/8"BSP Straight Female to attach the hose. If you have to use this fitting too, note that it isn't available in stainless (suffix 'C'), but you can have it supplied with a stainless hose nut.
4. At the engine end of the hose, I used a 5097-03C Banjo Side 20-degree Extended Neck to curve the hose towards the frame tube.
5. To attach the banjo to the engine, because I wanted to retain the o.p. warning light, I converted a switch to be a banjo bolt too.
The standard switch has a length of 1/2" o.d. between the hex. and the thread; I had a local machinist turn this down to 0.405" (the max. o.d. of the thread), drill a hole across 3/16" down from the hex. (this'll match the hole to the hose in the banjo) and relieve the circumference of the switch in line with this hole.
If you want to use a normal banjo bolt to mount the banjo, you'll need to have one made up, unless you can source a banjo bolt to match your engine's o.p. switch thread - early '69 ones are 1/8"NPT (National Pipe Tapered), anything later is 1/8"NPS (National Pipe Straight).
Btw, the banjo bolt hole will need to be opened up - it's intended for a 3/8" or M10 o.d. bolt.