I looked at a 40 with a single engine that the owner had the tanks replaced professionally. One side at a time (1 per year) , and by two different yards.
This was circa 2004/5 and the cost was about the same, it was right around 10K in Connecticut.
They put in two approx. 50 gallon plastic tanks per side, with separate fills and I think they were plumbed together in pairs at the bottom.
That's about all I remember. (The rest of the boat was a mess so I didn't pay too much attention)
So far (knock on lots of wood) mine are still ok.
However IF and WHEN I would cut them up myself and remove, and most likely go with poly tanks as PS has done. But I'd probably go with more than 58 gal per side, but would definitely not put as much capacity as I currently have. 360 gal is way too much for a single engine trawler with a 120 Lehman.
I would use the saved space and weight for extra fresh water and "boat junk".