good work. test that blackwater tank (mount the dump valve if necessary) before you put it back in. If it's the waxy plastic (smells like a candle when melting) you can weld any cracks:
'69 Safari bath floor repair
don't know about fixing the others. not a bad idea about taking out the aft part of bath floor. many have done it and glad they did. the fiberglass bath parts are also repairable and paintable to a nice bright white.
keep up the good work!