I had the identical problem with a Thornycroft marine engine. It too had been immersed in seawater for a very long time. It actually looked restorable from the outside, but inside was another story. The crank,cam,rods followers and pistons had become one piece. It was obvious from looking up the bores that it was an insurmountable problem so I promptly gave up! I advertised it for spares and a guy in Australia actually sent a cheque to buy it but unfortunately , while in "storage" it fell fom it's pallet about 25 ft onto concrete and solved a lot of problems!!! Only the brass parts were salvageable and they were sold at the 1000 engine club stall. When it was in "pieces" it was even more obvious that the job would have been impossible. The remains of the pistons still had lumps of bore "welded" to them and the mains were still firmly fixed to the crank.
18 years ago