Can one assume that if the hell hole rot and rust has not eaten through the top of the long that the internals of the longs are good?

chances are good, but assume nothing ...

sometimes pinholes can be hard to spot ...

how is the underside and the jack post area? lower firewall? floor pan behind pass. seat?
Andy

Yeah I figured to be worried of pinholes and such.
The outside of the longs appear spotless. Not even discolored paint.

But... Driver's rear quarter pan is swiss cheese. Passenger rear has one small hole right in the corner where the firewall and long meet.
Should I have the my welder open the top of the long(s) to take a peak? Or just leave as is?

you know there is a drain in each "long pocket"

post some pics