Just a suggestion........ I remember rebuilding an 84' 6.9 which was prone to cracking the block. My father didn't want to waste the money on getting the block checked for cracks. We got it rebuilt, never ran right, and the crank broke around 20k later.
We pulled it apart, and there was no testing necessary, the heads were visibly cracked, the block was visibly cracked, and the crank was in two pieces. Talk about a serious bummer!
Look on Craigslist, and get a running engine for under a grand; hear it run before buying.
By the time you get your current engine out, you'll be familiar with the setup enough, to install a temp engine while rebuilding your 6.9.... you can also just run the 'temp' engine for as many miles as it'll go until you can build the engine you want.
If you do rebuild your engine, follow the advice of others here.