I have a 76 I-28 also that I have been working on for a few years now. I am retired but one of my former lives was a boat builder and might be able to offer you some suggestions. It is a very comfortable little boat to start on. Perry considers it one of his best designs and is worth the investment in time if the boat is generally sound. The cabin soles (floors) are easily removable. The frames on my boat were and still are encapsulated in fiberglass. Running a drill through them reveals punky wood that I will probably replace at some point but there is so much glass over them the glass has effectively become the frame. The center floor boards should be loose and removable anyway for bilge access.
In my bilge the engine space connects via two 1/2 inch tubes running on either side of the space below the floors just aft of the main bilge. I suspect this is a rebuilt version of the original design. My emergency bilge hose is stored under the galley storage drawers and only gets deployed if needed. I added a bilge pump hose to the original set up that connects to the A-4s raw water intake plumbing. If I need an engine driven bilge pump I can shut the seacock and open a second valve so the raw water pump sucks from the bilge. I routed this hose beside the existing electric bilge pump hose. The existing hose passes aft through a frame near the floor and along with the new hose exits the bilge space near the base of the port settee and then is routed through the bulkhead that supports the stove counter. It then passes through a hidden bulkhead and back under the sink then aft under the battery shelf along the fuel tank support bulkhead. The new hose exits the space under the sink into the engine space where it connects to the raw water plumbing. I did not have enough room to conceal the new hose along this path so I simply let it show where the cabin sole joins the settee frame. If you want any suggestions about how and what i have done send me a pm and I will be glad to give you a hand. I have sailed many small, up to 60') sailboats along the Maine coast over the past 35 years and the I-28 is one of the best. Congtats.