400 Block...what to look for?

I have a lead on a complete 400 engine for sale near me for $250.00
It came out of a 76 Cordoba with approximately 80k miles.
It has all of the pulleys, belts, ac compressor, complete from oil pan to carb.

I don't want critiques that I should avoid it or pick a different engine. I've already read all of those debates:).

What I'm interested in is if y'all have advice on any specific casting numbers or other possibly 400-specific things to look for.

More importantly are there any cardinal-rule items to avoid if they are present.

Once again...thanks. as always...this site and it's members are great.
Hopefully, if the purchase works out....this will be going into my 69 dart. :toothy10:

Thanks,
Stepper