I'm pretty sure I got it from the Restoration Designs site - they have a few of the factory workshop manual dimensioned drawings available for download.
Restoration Design Inc. | Videos & Media
I've got a bunch of them printed out on 24"x36" paper on my shop wall for reference... super handy!
Again, it may be for a SWB tub, which may or may not be the same as a LWB tub! I can verify a few dimensions on the '74 I have over the weekend...
Tom