Welcome to the ZR-1 Net Registry Forum!
The sleeves can be replaced. If it was overheated to that extent, the damage could also extend to the cylinder heads. Overhauling an LT5 engine without having LT5 experience can be an expensive learning process.
You might consider buying the engine, if it can be had for cheap, then tear it down and inspect everything to see what is still good so you can prepare a shopping list for what would be needed to fix it. Then, if you decide not to repair the engine, salvaging the good parts would probably get your money back.
You have come to the right place to seek information. If you decide to proceed with the engine, posting photos and asking questions here will be your best choice.
If you want to shop for parts to see what things cost, I have new & used LT5 parts for sale that will give you an idea of cost. Here's a link to my website. You can contact me directly with any questions if you like.
www.jerrysgaskets.com
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Jerry Downey
JERRYS LT5 GASKETS & PARTS
http://www.jerrysgaskets.com
1994
ZR-1, Black/Black, Lingenfelter Aerobody, 416cu in, 3.91 gears, coil-over susp, Brembo brakes, etc.
2016 Black-Red, 3LT-Z51 Auto 8-speed.