83 300SD Turbo Rebuild Question

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I was quoted a price of $1000 to rebuild my turbo to factory or $1300 with higher grade parts (he is also talking about boring it out for this price) and was told I could expect a 50% increase in HP. I must say that if this is true 50% for that kind of coin seems like a good thing, but I am out of my league here. 1. How do I know if I need to rebuild the turbo (don't know if it has ever been done)? 2. Is the price good, and is the expected HP increase realistic? 3. What other concerns should I have prior to allowing this work? The car starts and runs good, but is extremely slow off the line (expected). My goal was to try to achieve a little better pick-up to stay with traffic and stop seeing the "bird" in my rear view mirror. :)

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