Hello Dan,
Here is a link to show the spin-on type and the canister type. Some people have welded a drain bolt onto the bottom(see photo album) to pre-drain the canister and then remove it.
http://6066gmcclub.com/forum/album.php?albumid=63
The actual process is not bad just potentially messy.
Have a pan underneath to catch oil as soon as you loosen the center bolt. It does have a spring and might have to be tapped to give way. It will drop down but should still be attached so you can wiggle a bit an slowly lower it down.
Make sure to get all the gasket out (big O-ring thing) so when you go to replace it, it's seals properly.
Put your new canister filter inside and fill with a bit of oil and bolt it back up.
Then try to find the spin-on factory unit.
Have a great day, Henry