Cable connector question

Hi everyone and happy fathers day to all who qualify!

I am finally upgrading my inverter to a Xantrex ProWATT 2000 that has 5/16" bolts for the DC inputs. On the battery bank I am using a Blue Sea Systems Dual MRBF terminal block with a 300A fuse that has 1/4" bolts.

To connect the inverter to my battery bank I am having some cables made by Genuinedealz, I'm going with 3ft of their 4/0 AWG marine wire. Using their custom configuration tool there is not an option for a "Heavy" walled tinned copper lug connector in the 1/4" size, the "heavy" connector is available in the larger 5/16", 3/8" & 1/2" sizes.

Would the standard 1/4" lug be acceptable?

I've got an existing 4 AWG cable with one of the "heavy" 5/16" lugs and it fits fine but I don't know how much larger one of the heavy 5/16"lugs for 4/0 cable would be and if it will fit.

Assuming it will fit, does anyone see anything wrong with using a "heavy" 5/16" lug instead of a standard 1/4" lug on the MRBF side of the cable connection? What about using the 3/8"heavy lugs on the 1/4" bolt (to be able to repurpose these cables in a future project as my hardware is upgraded)?

Thanks for your input!
Howard