Should ? no clue, Retro Spec ? it is not a known crank, who are they?
get several lengths .. to make sure , and return the ones that don't work ..
Generally,
Low profile cranks use a short spindle, often symmetrical
wider profile type sit out further , come back in, use an Asym BB..
and need a longer spindle to place the chainring in the same place
the right angle type take the longest spindle. but can be lowest 'Q'
The crank is Retrospec 3 piece crank.
Guess if Jenson sold you that , go with what they said.