Hi Prahlad,

Some time back I had a first hand experience of trying ( in vain ) to replace a INA105 ( precison unity gain diff.amp) with a discrete set up with 4 nos of matched 27kOhm rsistors. ( INA 105 not available - m/c had to be put back in operation ). Here also the abosulte value of the resistors does not matter as much as the variation between them. If you read the data sheet of INA105, you will realize the criticality of the ratios - even though all four laser trimmed resistors on the chip are equal, two among them are "more" equal to each other !

Finally peace prevailed when the discrete set up which was managing the show for a few days was dumped and a fresh INA105 was put in place.

SO it would all finally boil down to taking a calculated risk - try it out as outlined by you and if the results are in line with expectations, leave it at that.

Raghu