Yes, engine must come out.
SS tank would be nice, but not needed. Most steel ones live on nicely with regular use - hint
You - may - be able to have a good radiator shop fix yours.
Otherwise, call the vendors and see what they have in used or new.
Your sender is $$ from the vendors, so try to repair it to working condition. Recently, we learned the sending unit from a Fiat X1/9 is a very close match and can be used with minor modification.
I suspect you will have more questions if that engine is coming out - we'll be here
Larry