You could also consider a more modern 4L60E from a newer pickup or G van. They are a newer version
of a 4 speed O/D with lockup converter. Much easier to find now than a older 700R4.
The recycle yards are full of them.
They were made with a one piece case or a two piece with a removable bell housing to fit different engines.
There is also three series of them.
The other 4 speed O/D GM that most folk ignore is called a 200 4R. they are a direct swap for a Powerglide.
Some think they are weak but they were used in Grand National Buicks, Monti Carlo S/S, and full size Caddys , Buicks & Olds.
I would love to put one behind a aluminum 6.0 Ls engine and swap the whole thing into one of our Volvo V90 wagons.
I have a 4L60 and a 5.3 from a 06 pickup that might go into my 62. My wife will then have a automatic to drive. Swapped my old Goldwing for it.
Happy wrenching.
Howie
