BB 727 to A518 Conversion

Unfortunately it's not as easy as that. But what a great thought!! Essentially you are correct that the basic housing will accept some of the 727 parts. Where the cases differ is at the rear where the OD housing bolts onto. With the 518 housing there is a recess for the OD Clutch piston, also the govenor support is way different. You will also need a different flex plate if I remember correctly. Rusty Rat Rod is the Guru on the 727/518 conversion. He will point you in the right direction.