Project is alive and well but slow. You can go to 96.5mm/3.8" on cylinders and still have .175" thickness on cylinder walls but I would not go bigger because there will not be enough room for the heat ring by the middle head bolt. You will need custom pistons and the required 5.6 crank/rods.
Next detail I am addressing is the head gaskets. I have an outfit that can enlarge the bore with new heat rings on 4.5 gaskets. 5.6 gaskets are a different thickness and would require modification so I don't want to use them. If you have read through the post you have an idea of what is required. In theory pretty simple but some details that need working out. This is common place in the rodding world but most parts are off the shelf-it's just choosing the correct combination of parts. I have another thread on the pistons you might check out.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT