Hi,
The pan you have I believe should work, the center sump pans are more centered, I tried to put a 430 from a 67 Electra in my 65 a year before I went the nailhead route, and I had a center sump pan, hence 1 of the reasons it never got installed.
I thing to note there are 2 positions you can install the motor mounts on the block, I believe you need them on closer to the trans but can't remember, as it was 12 years ago.
Good luck with the project
Regards,