Starting engine, 12 years since run

Barn find, 63 Valient; Engine does turn, its a slant 6, told it ran before retirement, it has been 12 years since. Do not want to put gas in the old (sure it is foul and dirty) tank for the fresh start effort, can I drop a line into a fresh can of gas just before fuel pump to by pass old tank? Has fluids and fresh oil.

Any other cautions. Any suggestions. John