I run the 55 on my Wareagle stick steer. Little longer and probably a little heavier than yours. I run 2 group 27's hooked together and find that 90% of the time it more than sufficient. I pull cranks with my big motor and tie the stick off with a bunge cord then sit in back and steer with the terrova. I see no need for the link at the added cost. Cost/ benefit ratio is way off for most of us. I would do like Wannabe said and build a shelf for added battery and go with 31's. The 27's are all I can fit in my boat since I run a 27 cranking also. I might also look at going with 1 golf cart battery. With money saved and your budget I'd get the helix 10.
Proud Member of Team Geezer
Charlie Weaver USN/ENC 1965-1979