2 Engine Swap Options - Advice?

[greywurm]

My '71 has a 250 in it with a small crack in the head around the temp sensor that leaks coolant slowly with a JB Weld patch job. I'm looking to swap back in a 350 (PO replaced original 350 with the 250).

I have a couple of local ads, both im pretty interested in, but am unsure about the first motor's performance. From some research on the block number, I think it is either the LT9 or LS9, the LT9 sounds like it isn't very good unless I were to change the heads and cams. Block number is 14010207, the seller says its from a 79, but the block number tells me its an 80. Anyway to tell whether it is the LT9 or LS9?

It's a complete motor minus the starter and carb, supposedly was rebuilt and sat for 8 years because he never got started on his project. He's selling it for $400, $500 if I want to grab the TH350, or $1500 if I also want the 79 truck which I dont really want.

An alternative is another 350, complete minus pulleys with edelbrock intake and carb, block number 3970010 with th400 for $600. A little further to drive though. Seller said mileage is about "5-7k weekends only to car shows local swamp meets was in my 57 pick up with turbo 400 with shift kit ran good, replaced with a 5.3, no pulleys used that set on other truck"

I think I might be leaning to the 3970010 block, especially with the better tranny and a better chance it isnt the under powered LT9. What are your thoughts on these?

Is it much work to change from a th350 to a th400?

Thanks all.