The UC300ETH could interface directly with your existing parallel BoB, provided you have a 26-way IDC to 25W-DSub ribbon cable (I think one comes with the UC300ETH - you to check). Obviously it means sorting out the physical layout to support this - you to check.

The UCSB BoB is a high quality, robust BoB, nice design but at a price. If your existing BoB works robustly with you machine then I wouldn't rush to replace. If you was in this game (of replacing) then I've suggest looking at the AXBB instead of the UC300ETH/UCSB combo to see if that would match your needs.

A laptop charge would work for the 12-24V supply.