2000 wit hblown head gasket

Ok so Last week I purchased a 2000 3500 dually 2wd to tow my new boat. It has exhaust, air raid intake, and some banks gauges. other than that I am assuming its all stock. Except it liked to roal the coal big time when I would get on it.
Well I was towing it to the lake this weekend and on the way there it started to over heat so I pulled over and put some coolant in it ad when I pulled the cap it was cool to the touch and not pressurized. Cap was good. so I figured it was the thermostat. I changed the t-stat and low and behold the housing was bone dry! So I put the t stat in bolt it back up and fill er up. Well not to long after that it started over heating again. the nthe can of worms really started to spread out. there was a coolant leak the size of niagra falls coming from the rear passenger side from between the block and the head. I kept putting water in it and crippled her to the lake. ( I was more than half way there already) well whenI was almost at the lake my oil pressure started to drop. I shut her down and let her cool for a bit. turned her back on and the oil pressure was ~25 (guess from stock gauge reading) @ idle. I had to cripple her back home as well keeping a close eye on the temps and pressures. I couldnt keep water in it for more than ~20-30 miles but the kicker is as I drove ~60 mph the oil pressure would drop slowly then I would have to pull over and wait for it to cool and add water ( i used ~ 30 gallons)

So am I correct in assuming this is a head gasket failure? There is no water in the oil and no oil in the water. but after I installed the t-stat the coal rolling I mentioned earlier had susbsided to almost nothing except in 5th @20 psi.

Also what do I need for a basic stock hg replacement? hg, exhaust mani gasket, intake mani gasket, and heater grid gasket? and some head bolts (no cash for studs) and also I am thinking tis is deffinately a pre existing condition before teh sale? other than this this truck runs and drives perfectly.