Number is not found in 1969 or 1970 MOPAR Parts Catalog. Number is not found in GG's "white books". Number is not found in Hollander interchange mannual.
It would be a late '60s part number, are you sure it is correct? Is the numbwer on the driveshaft or on a parts tag? Can you measure it & get dimensions?
That is the casting number for the aft u-joint cap. Check the other end and you will find a different number for the transmission end. The number you need is stamped in the tube and will probably be within 12-18" from either end. It will look like this, the date code is nearby.
The seller say the driveshaft came from a 1970 cuda 340 3 sp manuel , the dimensions is : lenght 43,85 inch, diameter 3 1/4 ,u-joints is 7260 in front and 7290 rear .