It depends on how many years "many years" is. The NJ treatment of 401(k) contributions changed on January 1, 1984. If all your 401(k) contributions were made after that date, the entire amount is taxable. If you rolled it over to an IRA, the entire amount rolled over to the IRA is part of the taxable portion of the IRA. If you never made any other contributions to that IRA - that is, the IRA contains only money that was rolled over from the 401(k) - then all distributions from the IRA are fully taxable. The amount you converted to a Roth IRA was taxable in the year that you converted it.
