Chevy & GMC Vans

I want to do away with the dual key set up of my 1987 Astro and get all new cylinders for the dual sided single key like my 2005 Astro.
I also want to have bots vans keyed alike.
Has anyone ever done this and posted progress information and photo's of how to do it.
I talked with a local lo9cksmith and he said it couldn't be done....I DO NOT BELIEVE THAT!
Can anyone supply helpful information?
Thanks

George, nice to see you on here. Things haven't worked out for me making it through SC yet, but one of these days I will be sure to call first.

The door cylinders don't seem like they would be a problem, but the ignition cyl might be.