It depends.
Assuming they are from about the same time of manufacture and were manufactured when the 6PL came with the P60L LED drop-in, then no, there should be no difference.
If the 6P incan is an older model without the notched ring retaining the window in the bezel, then that will be a difference, though. The press in windows were made of Lexan, while the 6P bezels with retaining rings use borofloat glass windows. I'm not sure if that difference would matter with a Malkoff M61 drop-in.
If the 6PL is a newer model with the LED integrated into the bezel (KX4 or KX4D bezel), then a replacement bezel might be needed to install the M61. (I think I read that the KX4/KX4D can be disassembled and have another drop-in installed, but the resale value of the KX4, compared to a regular Z44 bezel, makes doing so impractical.)