Trans gurus, need info!

Ok guys, I want to blend some old with some new, and I don’t know enough about interchange of parts to know how to proceed.
What I want to end up with is an overdrive version of a clutchflite.
I assume the easiest way would be to find a non lock up version of the 727 based a518.
So, if I can find the clutchflite conversion parts(anybody got some?) I assume the input shaft will be based on a ‘60s era 727 on the trans internal end. Is the 518 input spline compatible/ interchangeable between the two?
Am I asking the correct questions???
What would the trans core I need to do this be out of ?(year/ model)

I see some custom fab work in your future!

I believe all Clutchflite input shafts are made in the pre-'78 2-ring configuration. In '78 they reconfigured the input shaft and it's relation to the rear clutch piston retainer and the reaction shaft support.

To make the Clutchflite work in a 518 you'll need the pre-'78 rear clutch piston retainer, the Clutchflite input shaft and a pre-'78 reaction shaft support (pre-'74 is most desirable). Then the only problem you'll encounter is the bushing in the rear of the input shaft, it's bore is larger than the pilot shaft on the transmission intermediate shaft so some machine work in the form of a reducer bushing will be in order.

Thank you! That doesn’t sound so bad.
Now, does anyone have any Clutchflite parts ????

Contact member b1596 I believe he had a clutchflite for sale