IS the question "Can I put a Group 31 (or 29) in parallel with group 24's?"
If so the answer is yes you can, minor risk but this risks exists anytime you parallel batteries.
NOTE: on your Group 24's. I am told a GC-2 its in the same tray as a Group 24, (Check this first) but is a bit taller.
IF YOU HAVE THE HEADROOM, consider upgrading two 24's to two GC-2 They connect differently (Be aware of that) but again each pair of GC-2 make a single 12 volt battery 215-230 amp hours (Dependign on the speciic sub model) but that compairs to 150 for what they relace.. Replace in pairs.
Home was where I park it. but alas the.
2005 Damon Intruder 377 Alas declared a total loss
after a semi "nicked" it. Still have the radios
Kenwood TS-2000, ICOM ID-5100, ID-51A+2, ID-880 REF030C most times