Welcome to the board Gilbert.
If the truck originally had a manual trans, you will need to cut out the crossmember that originally under the bellhousing.
Then pick up a trans crossmember from any automatic truck from '63-'72, and bolt it up where you need it, an dshould be ready to go.
You might have to drill a few holes for the new crossmember. I had to do this on my truck.
As for the stering column, you can get one from a mid 70's Chevy/GMC full size van, these do not have an ignition key on the column, that way you can still use the original ignition switch in the dash. The main brace that holds it to the dash will need a some adjusting, but any newer column will need this.
But since it being a GMC, the wiring harness's are different from a Chevy wiring harness. Jolly's webpage should have wiring diagrams for the dash wiring for when wiring in the new steering column.
Make sure which ever steering column you end up choosing, amke sure that you get BOTH male & female connectors so it will be easier when wiring.
David