Transitioning from a Fish to a smaller Fishy-like board?

ok not sure if it's much of a "fishy-like" board, but I recently came across a JS Nitro 5'8" 19 1/4" wide 2 3/8" thick and was thinking about purchasing it. im coming off of a 6'4" 20 1/4" wide 2 3/4" thick board that i picked up from a garage sale that i absolutely loved! it was quite big and bulky for my size however.. had a lot of trouble duck diving it and turning it at times. i did manage to catch waves just fine with it and paddled well with it. im 5'7" at about 135lbs. think it's too much of a transition? im from socal so i surf sunset/HB area and the occasional trestles. thanks in advance!