Steve, in my lay opinion, you would do step 2 in your Post #38, following the order in the charger's instructions as I linked in Post #39 [which should match the instruction book you got with the charger], and which I summarized mostly correctly.
-- New red/pos alligator clip to red/pos terminal where main AS red cable attaches;
-- New black/neg alligator clip to other battery's black/neg terminal where main AS black cable attaches
[Better to use the eyelet connectors if possible and get them bolted down under the nut with the other connectors, if possible]
240Ah would seem to cover both of your SRM-24 batteries IMO, but hopefully the shop will confirm.
If you are in doubt about any of this, after reading the manual, please wait for an expert to confirm the above.