That
Deka battery is, apples to apples, a 230ah battery. Basically the same as your new batteries. The 75 reference had me thinking small motorcycle size.
I don't know how old or degraded they are but if they're in decent working condition, really with FLA as long as you keep those paired they could be ok in parallel with the new ones. Monitor water consumption to know if the charge cycle is boiling some cells excessively.