I would never purchase a another seized engine, if your not able to rotate the crankshaft you'll never get the connecting rods into a position to access all the con rod nuts.
Oh god, tell me about it.... I've got a seized Jaguar V12 here, it's an absolute bear. And yes, only about 60% of the conrod nuts are accessible, and some of those can't be fully removed even if they could be loosened! I've got an old bathtub down at the workshop, one of these days I need to fill it with diesel and soak the block in it for a few days, in the hope that a soak + a few wallops with a hammer will free it up. Fortunately, I don't need the engine - just the heads, which came off after a brief fight (I won). But if I can disassemble it without breaking/bending anything, it'll be a useful experimental engine (I want to replace the cast iron liners with Nikasil coated aluminium ones - should be a considerable weight saving, and will reduce differential expansion problems). But that's a story for a day far in the future...
Once had a V4 with one seized piston that prevented full access to the con rod nuts, I cut a plate out of .500" steel then drilled in the holes to simulate the cylinder head.
Installed a grease zerk then using a grease gun was able to press the piston into a new position.
On another V4 had several pistons seized, I drilled these full of holes to weaken them to the point they could be smashed into pieces to fall into the crankcase.
Recently acquired another V4 Wisconsin three out of four exhaust valves stuck open, after removing the cylinder heads I heated the valves just enough to cause some expansion, then as they were cooling down added penetrating oil. that would be sucked down into the guides.
I would let the oil do its work for a few hours sometimes overnight then repeat the procedure, after a few days the valves were freed up.
The shop manual says to torque the head bolts to 25 ft pounds then repeat after running the engine, well this engine is instead going into storage and will not be run before hand.
I wanted to install all the shrouds (tin) that keep the engine cooled while running, again I used a hand held torch to heat the aluminum heads then after they cooled down re-torqued the head bolts.
I had never done this procedure before and was surprised that each head bolts being torqued actually moved another 1/8 of a turn.
Oh I reused the head gaskets, cleaned them up with sandpaper then gave then a coat of silver spray paint.