Sounds like a good project.

I'd guess you're going to have a hard time fitting the radiator inside the engine compartment.  Most V-8 swaps require some extensive remodelling of the radiator support to move the radiator forward and then end up running an electric pusher fan.  It's going to depend on what the front of the Buick looks like.  In particular, how tall is the water pump, does it have multiple V-belts or a serpentine arrangement, and how close can you get it to the firewall.  An alternate option is to renovate the firewall but then access to the back of the motor can become questionable.  If you want to have to pull and engine to change spark plugs, then just buy anything new from the dealership.

Whatever it takes, don't skimp on the cooling systems for both the engine and the transmission.  I ended up punishing a 4L60E behind my 4.3 Vortec for a little while and will be paying the price for it shortly.