what to look for - 91 Turbo 350

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new round heayah. Hopefully y'all will have some insight. Looking at a package deal with a 91 350 quad cab duelly. When I looked under the hood I was surprised to see a turbo. In reading, some can be good, some not so much. Guy that owns it bought it to move from Ohio to SC and knows very little about it. Blew the tranny on the way down. had it rebuilt with 'heavy duty parts'.

So, questions, what should I know about turbos. Seemed solid. I was impressed driving it. What tends to fail on them that should be checked out? Overall it seems to be in pretty decent shape. He wants $11k for it and 31' haulmark enclosed trailer. That seem reasonable?

Truly, I've been reading tons recently but it's difficult to find what's actually relevant and know what I'm seeing.

thanks!