Turbo 400 and 5.3 in a '69

[runpasthefence]

Hey guys, this is my first post and I just want to say this is a great site with a lot of great info.

I've got a 1969 fleetside short bed with a 396 and Turbo 400 I'm going to pick up early next week. I'm a outboard and marine mechanic with no real experience with this stuff, so i could use some help.

I'm looking to turn this thing into a daily driver, but a stout one. I plan to replace the 396 with a turbo junkyard 5.3. It looks like you can find these engines for $300-$800 pretty easily. I'd go ahead and do a 4l80 or 6l80 swap too, but I'm not made of money. This will be a progressive project.

My question is, what's involved in making the 5.3 and turbo 400 mate up? Is a spacer needed?

Thanks