You said in another post that other then hard starting and steam in the exhaust the engine ran and revved fine,when you bought the truck you talked about it starting in under a crank and you didn't say anything about it running bad,smoking,knocking ,ect.... Now all of a sudden you think the engine is blown,since you already got all the parts why don't you replace the headgasket and see what happens
If you worried about a bent rod,which is unlikely just roll the engine over and make sure all the pistons have the same deck height.