chevy to gmc tranny swap

[wc63]

my friend has a 283 chevy with a 3 on the tree he wants to make automatic. i have a 305 v6 gmc and want to keep it 3 on the tree but dont like the low gears on the highway. i max out at about 60mph. does anyone know if the 3 speed chevy tranny will work with the 305 v6 gmc. i was told if the bolt patterns match on the bell housing it will work, but i dont know if the gearing difference will affect my stock rearend. any help is appreciated. i dont know if it matters but both trucks are 1963.