I have a question on an ad I found on craigslist of a 95 z28. It claims to have a 6 speed automatic transmission, which I find strange, because typically they came with a 4l70e, which is a four speed. Is this type-o or did they have a 6 speed auto? Also, the pictures that were provided didn't show any z28 bages.

What's the most amount of miles on an Lt1 that would be safe to purchase?

 

The automatic in the 4th Gen F-bodies from 94-02 is the 4L60E 4-speed. There is 6-speed manual (T56).... maybe that's the typo.

On the other hand, people have transplanted just about anything you can imagine into these cars over the course of 10-20 years.

There are people on this site who have put over 200,000 miles on the LT1 engine with limited problems. Others have suffered failures like the Optispark distributor in less than 100,000 miles. The rotating assembly seems fairly robust, but it's going to depend on how well the vehicle was maintained.

Get the VIN and run it through this site - it will give you all the options on the vehicle (at least when it left the factory) and the build date:

Comprehensive Chevrolet, .... VIN Decoder