Over the almost 10 years participating on the Cherubini forum, I don't recall any other 36 owner(s) posting about the diesel tank removal.
Your 1980 built boat #7 and my 1980 #36 are likely identical. More than a few times, I have stared at the diesel tank with trepidation -- for the day it might start to leak.
Since I can't add anything from definite experience, all I can suggest is what you have probably already contemplated. Contort yourself down underneath the port side lazerette and measure both the tank's LxWxH and also the dimensions of all aspects of the tank's possible "escape" routes. On my boat, the batteries are located underneath the port lazerete just aft of the ice box. Also the external heat exchanger is mounted there as well. These items will almost certainly need removal. Further, it is possible that removing the engine's containment box on the port and aft side might allow enough extra inches of manipulation room in order find a way out for the thing. Certainly, if the size of the lazerette openings are smaller than the tank size, then ...
... I have seen info here-and-there about alternative solutions such as cutting a hole in the side of a leaking tank, wire brushing the bottom, then laying down a bed of epoxy to seal. Or even injecting a bladder into the tank. These options I think would require a specialist to be confident of a successful outcome. Another option might be to somehow cut the tank apart into a couple of smaller pieces so it can be removed. Then replace with a new plastic tank somewhat smaller that would fit in easily. Or maybe two smaller tanks combined so that the total storage remains the current ~30gallons.
Good luck. Let us know how you did it! I am sure that other models of Cherubini Hunters also have tight tolerances for the fuel tank. So your recount will be useful to know.