2 GSP in 65 Gallon for life?

[Josehp Pepe]

I have recently brought home a pair of half an inch GSP. Now I've read plenty "Yes 2 will be fine in 55gallons" and also plenty no's to that question, with people saying no less than 75 gallons for 2 in some cases.
I have a spare 65 gallon tank (240L) 120 x 50 x 40 (cm) / 42 x 20 x 15 (roughly in inches) and was wondering if this will do for 2 GSP for life. I was considering this tank as it has more depth than height to it.
If this is however not an option, would a 50 gallon (195L) tank with dimensions 130 x 50 x 30 (cm) / 51 x 20 x 12 (roughly in inches) do for one puffer. I am unsure because of the low height on the tank if this will be enough for the pufferfish.
Currently I have a variation of small catfish living in that tank as it seemed suitable for a bottom dweller tank due to it's big footprint. If this will be OK for a single GSP (incase of 65gallon not being OK for 2 GSP) I could move the catfish to the 65gallon (as of now the 65gallon is empty). Of course the odds of them not getting along later in life are possible, so in that case I would also consider the 50gallon for a single GSP if the height of the tank will be OK for the fish.

For now the GSP are in my 55gallon brackish tank together with my figure 8 puffers and knight gobies (Don't worry, the figure 8's and gobies can't reach the GSP!) until I've figured out the best place to home those 2 little guys.

[Pufferpunk]

Obviously, bigger is better! If you plan to go. Water, which would include 1 1/2 to 2 lb live rock per gallon, you're going to want the 65-gallon for swimming room.

[Josehp Pepe]

So a 65 Gallon should be fine to house 2 adult GSP in for life if they'll tolerate each other as adults? Worst case I'll already list one for adoption if a 65 is not ideal for a pair. Parting with it will only be harder later if I won't be able to keep it in the long run.

[Pufferpunk]

It'll be a little tight if you go marine & add enough live rock.