How do you set the timing on a 1997 Isuzu NPR with a 350 Chevy motor in it?

For mechanical time take of your distributor cap put your #1 piston all the way up on the compression stroke(TDC). Point your rotor button at the #1 piston . Disconnect the vac advance. reconnect everything use a timing light to fine tune it the light hooks to the #1 plug and the Battery. the timing marks should be on the crank pulley/ harmonic balance Just aim and turn your distributor until you hit what the book says. Good luck, and then reconnect your advance.