That looks like the preasurized system I have (had) in my '63 Avion.
I kept the preasurized tank when I re-did all the plumbing (Colorado Trailer == many split lines) because I liked it for all the reasons mentioned above. The origional compressor was long gone, but a cheapo $12.00 12v
pump worked nicely.
Another giveaway is if the tank's filler cap has a hose attatchment. This lets you fill your tank, which also compresses the air in the top of the tank to around 50 PSI (depending on your water preasure). I set my pump to come on at 25PSI and I could go most of a days worth of camping before it kick on. Unfortunatly, one of the welds failed on the tank, and the trailer became self cleaning. I just finished the city-side plumbing (hose inlet and drain) and just ordered a 21gallon tank off Ebay for around $60 after shipping that almost fits the space the old 10Gallon tank was. I will have to move the bunk frame 2" back, but that will allow a Full futon mattres to fit on the bunk now.
My only regret now is I have to cut a 2 1/2 inch hole in the side of the trailer for the gravity fill.
Long story short (to late) Enjoy the presurized tank while it lasts, it really was a clever system. But if you have any doubts about keeping it, replace it now while you have the bunk taken out in case you need to make any modifications to fit around the new tank.