Update: I got a late start yesterday so I did not get the leak fixed but did get the bottom plate cut. I cut a 7" x 7" square directly under the tram pump, roughly 1/3 the width of the 422. What I did was insert a couple of wooden slate between the tub bottom and the hoses touching the bottom of the tub. Then marked out the square and drilled four holes in the corners of the square. I placed a very reluctant wife as fire watch armed with hose and fire extinguisher monitoring the inside of the tub for flame. Then it was off to connecting the dots with a 4.5" grinder and a 1/8" cut off wheel. All went well except for my ability to stay on the line and my wifes understanding of what flame is. Sparks and smoke are not flame!
So I now have a 7" x 7"...ish hole in the tub. I figured that was going to to make it very easy to work on the bottom of the pump. Well I soon found that the hoses routed across this section of the tub are very stiff and move little so the clear path in is still blocked. The next thing I have to do is reroute the hoses. Once that is done I think I'll have it.