23 scepter fuel tank compartment

[scepter23]

Hi, new member here with a 1980 23 scepter, have a repair issue. The previous owner removed the forward of the two fuel tanks and installed a 60 gallon towards the rear. The tank was not properly installed, just placed in fuel tank compartment and poured some foam around it, no attachment to stringers ! My question is are there any bulkheads that were original to the build in this fuel tank compartment area? There is no bulkheads at the rear or front of the fuel tank compartment? Also what would be the best size of replacement tank (in gallons) for a single outboard future repower 250-300 hp?