Is it possible to upgrade the fuel tank from a diesel tank to petrol?

I have a pretty rusty one.

Yes you can swap tanks since both vehicles are W126 you won’t have problems fitting them all you have to do is swap the fittings under the tank I did it in a W124

w123 possible to put a petrol tank in a diesel car? I know reversed it cant be done.

The only difference is the fuel line mesh in the bottom. Any W123 tank can be swapped into any other W123 (ie sedans of course...wagons completely different)

FWIW my daily driver is a 280 converted to a 300D.

__________________
1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD

yes I will swap over the level guage and a new tank screen. Yes its sedan.

I'm not aware of the fuel sender actually being different, but worth taking out for inspection at least

__________________
1978 300D, 373,000km 617.912, 711.113 5 speed, 7.5mm superpump, HX30W turbo...many, many years in the making....
1977 280> 300D - 500,000km+ (to be sold...)
1984 240TD>300TD 121,000 miles, *gone*
1977 250 parts car
1988 Toyota Corona 2.0D *gone*
1975 FJ45>HJ45
1981 200>240D (to be sold...)
1999 Hyundai Lantra 1.6 *gone*
1980s Lansing Bagnall FOER 5.2 Forklift (the Mk2 engine hoist)
2001 Holden Rodeo 4JB1T 2WD

the other tank I have seen has no level guage and screen just a bare tank.

The fuel sender should be the same. But how are the air vents arranged on the two tanks? Diesel tanks usually vent to the atmosphere, gas to an evap system.

Looks the same to me