I have successfully used Turbo Boost gauges as fuel pressure gauges, although if the fittings are not tight, the fuel can travel up the hose and cause needle jitter.
To allow it to monitor the pressure of both fuels (I use separate fuel pumps and filters for my start fuel and veggie), I installed it at the IP inlet.
Dedicated fuel pressure gauges are available on eBay and should be suitable for this application.

Tony

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Tony from West Oz.
Fatmobile 3 84 300D 295kkm Silver grey/Blue int. 2 tank WVO - Recipient of TurboDesel engine.
Josephine '82 300D 390kkm White/Palamino int.
Elizabeth '81 280E, sporting a '79 300D engine.
Lucille '87 W124 300D non-turbo 6 cylinder OM603, Pearl Grey with light grey interior


Various parts cars including 280E, 230C & 300D in various states of disassembly.