The major problem you might have is if the SCSI card is sodered on to the board of your G3. Some models have a pull out card, some do not.
Open the G3 and check it out. If it is indeed a pull out card the next thing you must do is check the G4 for an open port that can accomodate the card.
The next trick is to find out if the new machine will run your SCSI equipment. What OS are you running?