An LT1 is a SBC....
Crate engines will likely be your cheapest route, and you will get a warranty.
Any used engine (LT1 in your example) may be a good way to go, but yoou won't likely know the history.
My recommendation (FWIW):
Get a running 350ci donor car for cheap....find something that has body damage etc.
Swap into the Z and get everything working. Upgrade your suspension, brakes, chassis etc.
After some time working out all the bugs etc, pull the motor and hop it up if you want more power.
Tim