Sorry can't help you with the right shop/etc. But, I did notice you have a boat that's is similar to mine although a bit bigger. I did the Boysen reed thing myself and and it seemed to help slightly with mid range (89' merc 200). I also put solid motor mounts in mine. After two seasons of living with them I am going to pull them back out. The added vibration that ripples through the boat from 5 to 20mph wasn't worth the gains in steering etc. considering I use mine as a "family" boat. My 18' Lavey, possibly unlike your 20' has the motor mounted on a 16" setback which I think at that length amplifies engine vibration thru the hull with solid mounts. I was going after getting rid of some 60+mph chine walk. Changing props and putting the motor up a hole on setback was more effective.
http://www.***boat.com/image_center/...er_008-med.jpg