Testing the Integra's power
 

Is there anyway to test a GS-R to verify that it has retained the same power as it was brand new?

Compression Test.
Leakdown Test.

Any competent mechanic should be capable of these tests. Are you suspicious of abuse by the previous owner? :dunno:

how much woud that run me?

You can buy a compression tester at auto parts store for 30-40 $US, or alternatively, you could spend a lot of dough and put it on a dyno

You can probally dyno for around $40-80 an hour. That would be your best bet.