Look under the engine mounts on the outboard sides. Open the engine hatches and stand outboard of the engines, on the hull, in the engine room. Then bend down and look at the fore and aft hull stringer stiffener welded to the hulldirectly under the outboard fore and aft engine frame mount, on the bottom. Compare this engine mount edge to the fore and aft stringer-stiffener. If it's parallel with the bottom of the engine mount, the hull probably hasn't gone thru much stress and has some life left in it. If the stringer is bowed upward, the hull has been pushed hard thru waves and probably been airborne. Yes, you can get a 41 airborne. Don't ask me how I know this.
The hull is aluminum, as you know. Aluminum has no fatigue life, and it will crack regardless of how light the loading if it is stressed repeatedly enough. This is how Boeing stays in business. The series of Aluminum on the hull was a 5000 series, it's not hard to find out exactly and what the fatigue and strength properties are of that aluminum. It's available as sales information online for sure.
Making this worse are the great v8 turbo engines in the 41utb, they're big, heavy, and powerful. The Cummins 903 engines are governed down to only 300hp, they are capable of higher outputs, Cummins rated some 903 versions at 400hp. You do not want to pursue more power, this will stress the hull higher and make it fail faster. Cummins does not make the 903 v8 any longer, which when combined with the aging aluminum hulls is the reason the USCG surveyed the hulls and sold the boats all off, as great as they were. (sniff.)
Somewhere, the USCG has an engineering report on the hulls. You may want to use the freedom of information act and ask USCG engineering for that report. It's around. It exists. The USCG does not get rid of anything they don't absolutely have to, they get lots use out of their equipment.
One relative way of determining the potential life of your 41 utb hull is to find out where it was stationed throughout its life. If it was a quiet USCG station with a low search and rescue case loading, then this is the best situation for you, the hull will have lower use. If it was a heavy use station with hundreds of cases per year, then it has more fatigue cycles on it. Also, be aware stations in northern climates that iced pulled their boats in winter, the aluminum hull cannot handle ice. The worst 41 utb to have from a relative perspective would be one that spent its life at a temperate climate, a warm station, in or near a large city, toward the south. For example station Miami had about seven 41 utb's and they ran the hell out of them, Miami was the busiest station in the country, and probably still is.
If you have such a high use hull with bowed plates and stringers, I'd look to get the metal tested, which means taking metallurgical samples at high stress locations, and having a reputable metallurgist, say one that does consulting for Boeing or one that works for Boeing, do a fatigue inspection on the sample. If you've got a high time hull, that will tell you, and there are remedies, remove and replace sections remedies... i'd be careful about adding more material to stiffen a section you suspect as weak, that will just assure cracking where the stiffening stops.
Do these checks, stay out of surf, drain the fuel tanks, open the tank access covers (aft, in the lazarette compartment), ventilate and clean them out. Do not 'drill a hole' and connect the two port and starboard fuel tanks, if you have fuel contamination you'll make sure you lose both engines if you do that, and it will detract stability, the upper tank will drain into the lower one, increasing free surface effect and making you less stable in roll. Most 41's spent their time with fuel tanks completely full, on the supplied charger, (forward in the engine room, starboard), with engine heaters on, so you shouldn't have interior corrosion problems, keep the engine heaters on. Opening the tanks is to clean them, you may find quite a bit of sediment. There's no way the engineering guys opened the tanks to clean them prior to surveying the boat out to you.
Also, boat stands were widely available as all the northern 41's were pulled regularly because of ice restrictions, look around and find them, they're big grey painted monsters, built with 6"x10" hull conforming beams, you'll want them for haul out, you'll need a forklift and flatbed to move them, but you shouldbe able to get them for cheap, for scrap value. Disconnect the shafts from the reduction gear if you do haul, before you haul. The reduction gears are stout twin disc units, simple, heavy, durable, they have a 'come home' feature you can use to lock down the clutch pack if you have a hydraulic failure in the gear, which only works on the starboard engine. There are two clutches in each gear, get the manual, figure it out, the port gear uses the opposite clutch for forward. The engines had a hell of a lot of torque, and we often pulled vessels much larger than the manual rated us for, and pulled them at 7-8 knots, the 41 pulls like a tugboat, so be careful with those throttles. Anyone who ran one will tell you they maneuver extremely well.