A federal court jury in San Francisco convicted Shaun Small of possessing and exploding a bomb he delivered in a bouquet to his employer's estranged wife--but acquitted him on a charge of having manufactured the device. Melanie Pilaski, 42, a contracting officer for the U.S. General Services Administration, and a co-worker, Pamela Castro, 42, were injured when the bomb exploded last Nov. 17. Assistant U.S. Atty. John Lyons said he would call Small before a grand jury investigating Peter Pilaski, his former boss and alleged homosexual lover. He said Small's willingness to testify could affect the prosecution's recommendation on his potential sentence of 30 years in prison and a $500,000 fine.