I just installed a new Groco HF head on my 86 27 tall rig. I'm very dissapointed with this product. They don't send instructions with the kit. It took about 7 hours of trial and error to install. The base doesn't allow a clear path to the tighen bolt heads mounted into the deck. The bolts for the bowl to the base are too long and interfer with the bowl. You have to install 4 bolts to attach bowl to the base. The back bolts are very very hard to get access too (The seal looks very inadequet} One lesson learned is that the deck is not hollow in the head and self tapping screws in a new location will work for monting base. I had thought that the base bolts were through a insert in the deck. I would think twice about installing the Groco on a Catalina 27.