I moved the battery from the back to the front when I changed engines from a turbo rotary Mazda to the lightest of Lycoming O-360, a narrow deck conical mount unit from a helicopter. I think the motor mount is lighter than the Dynafocal ring mount too. I used every light weight part I could, Superior cold air sump, and Airflow Performance fuel injection. I reduced the aircraft weight 71 pounds.
The battery cable from the back was weighed after it was removed, greater than 3.1 pounds!
I removed a 2 blade CATTO, and installed an 3 blade CATTO.
I mounted the cut down battery box on the fire wall, similar to VAN's plans. I still use an Odyssey PC-680 battery.
I wouldn't mount any weight to the crankshaft because I plan to do aerobatics and don't want to add stress to the crankshaft.
Right now, I should carry 25# ballast in the forward baggage locker to carry a 200# passenger. Solo flight is a joy.
I can add an inverted oil system for a favorable CG shift if I eventually compete in intermediate aerobatics, but keeping the weight down is a primary goal, so no carpet or wall panels etc.
I wish I had installed Grove Aluminum gear...and I'm looking at lighter tail wheels.
I wouldn't put the battery in the baggage well, the firewall position is farther forward for your CG concern and safer in the event of a lead acid battery explosion or a LiFePO4 battery melt down. Also the baggage floor is one of the possible smoke tank locations, so you may want to keep that option open.