Retro fish sizing

Hi all - I’ve been looking to add a retro-style fish to the quiver for a while and I found a 5’8" x 20.5ish x 2.75ish Larry Mabile KG twin keel that piqued my interest. Thing is, I’m 5’8" 185lbs and on te lower end of the paddle fitness spectum. Am I right in thinking this may not be enough board for me (particularly considering I spend the vast majority of the year up here encased in rubber)? I typically ride a 7’8" Austin single fin or a 6’8" twin fin hybrid fish-ish shape.

Any feedback is appreciated, as if this isn’t the right board, I’ll be continuing the search, both used boards and perhaps through a local shaper here in the Boston area. 

In your place I’d go a little longer and a little wider; like 5-10 x 21".  The 5-8 would probably work for you if not for the extra rubber and the cold water.   Short + flat + wide + keel is already a tough combination to get used to if you haven’t surfed them before.   There’s no sense in giving up that last 10% of volume - that might be the difference between you getting your waves or not.   

Thanks for the feedback. I’ve picked up a few boards in the past that were not suited to my size / ability, and I think i was about to do it again.  

that boards sounds nice to me. but if you want more paddle power go wider and thicker. maybe 5`8 x 21 x 3. that sounds fun to me