From what I know about SBCs, a heavily scored lifter bore usually equals a scrapped block. Not sure about I6s
Is there a way that you could bore the lifter bores larger and use a different lifter that is slightly larger in diameter and make up for any height difference with a over/under sized push rod? Just an idea, I'm not a machinist.
Considering what you've already spent, I'd try my other options before tossing a bunch more money at another engine. By the pics, it still looks like you have a ways to go to finish your ride. So what's the hurry on the motor? Maybe you could use the spare time while working on other parts of the car to track down another block and move everything over.
If I was in your position, I think I'd give my machinist a call and explore some options.
If you do end up going the route of a rebuilt crate motor, and still plan on using the head off your current engine, I might be interested in buying or trading for the head off the crate.
