I have a '91 2.5 with 157k; I am interested in better performance and less turbo lag. It was suggested that I change injectors and possibly the turbo. Can you give me any advice.

I don't know who might have suggested changing the turbo and the injectors, but you probably will not get the performance you probably want, and you will make your wallet considerably lighter. My recommendation is that you don't open that door.

Now, on the other hand, with 157k on the fine turbo and injectors supplied by MB there may be some room for restoration to its original performance.

A few tests by a tech can tell you if your turbo is producing all the boost it is supposed to produce. There may be some injector pump work and timing work to be done to get all the fuel to the injectors that is supposed to get there, when it's supposed to arrive.

My $0.02: have the whole fuel system checked and adjusted properly first, and see if some of the turbo lag doesn't go away and some performance return.

Good luck.

BCingU, Jim