To the original poster:
Do you happen to know where your boat was built? Since you're on the west coast, probably in California. The Columbia 29 was the first boat built for Columbia Yachts, and it was built in CA. Your Columbia 28 looks very similar to my Columbia 29. Same coach roof and port lights, but the 29 and 29 MkII (of the 60's) were full keel, one foot longer, with an 8' beam.
I have a word of caution for you... But keep in mind, my Columbia was built in Portsmouth, VA, and with a different build yard, you may not have this problem.
When I got my boat, it was in pathetic shape, and anyone else I think would have scrapped it. The bottoms of all the bulkheads were rotted, the plywood cabin sole was partially rotted, and the settees port and starboard were practically crumbling apart. The boat had taken on water for a long time.
I hauled the boat out and began removing rotted wood, and I was astonished how poorly crafted my boat was. The bulkheads were only tabbed in with one layer of three inch tape on either side, and the plywood literally sat two inches from the hull in most places. Nothing lined up properly, there was no glassed in support under the compression post... everywhere I looked, I said to myself "This is how they built it?? This is horrendous!!"
I gutted my entire boat. All bulkheads, cabin sole, settees, head, quarter berths, everything. I lowered my shoulder into the main cabin bulkhead and it popped right out. (I'm only 5'6" or 5'7", about 150 lbs, and in shape, but not particularly muscular.) The settees were in such bad shape, I just kicked them in and put the small pieces in a five gallon bucket to take to the dumpster. But after removing the settees and bulkheads, only one layer of three inch tape held them in. The entire boat was built that way. Quarter berths, engine compartment, everything. That is not strong enough for cruising. At all. I've heard of many CA built 29s having the bulkhead tabs pop loose in the short chop of the SF Bay.
I'm rebuilding my whole boat, and because I gutted it, I'm changing the layout, but I'm overbuilding everything. I suggest if you have these lofty plans, any changes you make should be overbuilt. I follow the theory "Nothing too strong ever broke." I'll be adding quite a bit of weight, but to me, that just adds stability and motion comfort. I'm careful to distribute the weight evenly and keep most of it below the waterline.
Anyways, the point I'm trying to make is, pay very close attention to how your bulkheads and other structure are tabbed in. Also, if you have a leaky deck, CHECK YOUR CHAINPLATES!! My deck leaks, and I suspected my glassed in chainplates (ugh) had filled with water. For kicks, at the bottom of the chainplates, I took my 4" grinder and ground through the fiberglass until I saw a couple sparks, and sure enough, water pissed out of all of them. Needless to say, I'm not using those chainplates. If your chainplates are bulkhead mounted, your boat is doing better than mine. If they're glassed into the hull, be sure they're not retaining water. Even if your deck doesn't leak, they could be full of water. You don't know what previous owners had repaired, and to what extent they made sure everything was right. For offshore and extended cruising, you need to know and everything should be overbuilt in my opinion. I carry two anchors big enough for a boat twice my size, my bulkheads are twice as thick as they were and are tabbed in three times with successfully wider layers of 1708 biaxial cloth, and I've glassed in new floor timbers, a new cabin sole, and a new support under the compression post. And I have a new compression post. After installing, I think an overweight circus elephant could sit atop my compression post on a unicycle and it wouldn't give way. If you'd like pictures just for the heck of it, or if you want to know what any certain part of my boat looks like to compare to yours, I'd be happy to exchange pictures and offer any sort of advice. I'm not an expert and don't claim to be, but I know my work is solid and true, and if I'm unsure, I read and overbuild to be safe.
Definitely check your tabbing and chainplates, and if you can, the structure under your compression post. PM me anytime you'd like to know anything or to get some pictures.