5.9 switch

Hi:
Sounds just what I have been doing for the last few years. Including a 904. Just do the basics,: New Mounts, Oil pan and oil pick up change. It all bolts up.
As for the serpentine. I used everything except the power steering. And kept the Dak/Dang. Compressor, Alt., early style crank pulley. Had to make a few trips to O"R. to get the correct belt size. Also, went with a March underdrive pulley on the water pump. Due to having a 3.91- 8 3/4". Stock 26" rad. 2 row. ( My "75" had factory air and replaced the rad with a new one. ( Amazon. $146.00)Runs cool as a cucumber. No heat. Too many hoses, and I live in OK. where we average 95 degrees. in JUly. And electric fan.
Note: If the front end has not been updated in the last few years replace all of the rubber pieces. Torsion bars: "OLD" update them. Another item: Have the "K" member welded. I mean the entire circumference. Especially, since you have a convert. and add frame connectors. It is a nearly 50 year old car. It needs strengthening.
Good luck..