The only way I know is thru. the gas guage it's self. There are some very good instructions in Les Andrews VOL.1 model "A" ford mechanics handbook on page 1-172.
Also in Mike's"A"Ford-able parts catalog.
1st. thing, disc. batt..... 2nd drain gas down to aprox. 1/2 tank or below the guage.
It's not that hard of a job. But it sounds like you ether need the instructions or some help from one who has done it. Good luck.