PLEASE NO, don't do that!!!
Never substitute data from another bullet just on weight alone!! With some common sense, and experience doing so can be fine, but you need to be aware of potential problems. For center fire rifle bullets, the differences between a Speer 180 BTSP and a Sierra 180 BTSP is zero. BUT there difference from a Barnes 180 BTX bullet is immense!! Your example of substituting lead bullet data from jacketed is also a big no-no. substituting pistol bullet data is a bit different as the amount of bullet inside the case is directly taking away from powder cap where the ave bottle neck rifle has a neck for the bullet. its not directly removing powder cap. You need to look at the amount of bullet seated in the case AND its weight and its legnth and its construction.
With out knowing or at least seeing that bullet as it compairs to the 265Hornady SP. I would hesitate substituting the Hornady data, but that is the closest I can think of from here.
CW