Welcome. this isn't my era of Old's but if you drop on down to the vintage forum there is a group of guys that are dealing with these issues now.I believe the thread is Who owns a 47 -49 Old's or something like that they should steer you in the correct direction.

When you can post a few pictures of your ride, we love pictures....Lost in the fifties ...Tedd

 

You have posted several question in a number of forums as suggested you should combine you questions and take them to this thread. https://classicoldsmobile.com/forums...-own-them.html You will be able to link up with others working on you year of Olds.

I have install a Mustang front end from Heidt"s http://www.heidts.com/part/mustang-2...uspension-ifs/

and a Ford 9" rear end using Super Slide springs http://www.posiesrodsandcustoms.com/...slide_springs/

Others have used t a newer rear end adapted to the stock suppension with some modifications