Hi 66 the panel you are looking for can unbolted and doesn't have to be cut out but I'd be surpised if he wanted to part it out like that.  More Likely he wants to sell the whole car  It looks pretty rusty and to me its overpriced the way it sits.

maybe buy the whoel thing take waht you want and sell the rest again (although I'm not sure Prince Edward Island  would be any easy place to sell a half picked over car like that especially from such a distance)

As for the tranny I'm no expert on these but they came as factory equipment on many GM vehicles from the late 80's until they were super seded by newer versions.  The reason they were popular was that they had 4 speeds with the the top gear being an overdrive with a locking torque converter so made pretty good mileage.  They were notorious in the early years they were offered for not being able to handle much power but there are a few suppliers out here that know how to beef these up to handle very muscley engines and that is probably what you want to do. (Ie get a beefed up one)  I believe one of the suppliers is called Gearstar based in the USA.

Just Google TurboHydro 700r4 to get a history and availaibility on these.  Since they were offered with a lot of 350's they will tend to fit any other small block or big block fo that matter.  Love that GM interchangability!

 To run them without a computer you will need some special brackets and a kit but those can be obtained fairly easily. I got my setup from Classic Industries out of the states.