Sailboat to Trawler/Shanty Conversion (Ep2) 

I'd keep the walking level at the original sole. You will have to keep the keel and partially lower it underway to keep the rocking down. You could also add two small bilge keels so she'd sit upright at low tide . In addition You can add removable ballast in the form of sand bags, or even water jugs to stabilize Her. Super important to build as light as possible the higher You go so 3/4 inch ply is ok for floor level, but cabin top should be half inch or even lighter if You sandwich styrofoam glued between two layers of thinner ply or ribs to strengthen the top. You maybe cool to sit on the highest level but not walk. So save weight and make the cabin walk through to do forward deck work. Check out the way Jim Michalak and Phil Bolger designs use this excellent walk through cabin with open center design. Then You can seal that center opening with light hatched or canvas snap on pieces. Essentially You want weight down low and not much up high . To keep Her from rocking removable ballast bag or jugs to fill with fresh or lake water. And slightly lowered keel and or bilge keels will help but also look into a short mast installation with a used or old one that goes through the cabin, even off to the side a bit, and anchored to to floor so You don't need wire stays. Then look into a rig called a dipping lug or lug rig which can be easily made on the cheap. This rig will help You at anchor or under motor power and even sail down wind. The old 1930 English motor boats often had short rigs that can even be taken down or lowered quickly and easily by one man when going under a bridge or trailering. Very cool and worthy project which I've been thinking about for a long time. Above All...Have FUN!

Stability might be an issue now without the swing keel. Especially with a raised cabin top. You might need to put some lead weights or sandbags under the cabin sole.

look like potential

Id pull the whole deck and start fresh if funds allowed I have a 25ft oday im doing the same with.i have a m25 diesel engine thinking bout installing,removeng deck and 1800lb keel.

How high can you go with cabin before you risk the danger of toppling over when in the water?