Form 5498 has nothing to do with reporting whether or not your contribution was nondeductible. Form 5498 simply reports contributions. To treat the contributions as nondeductible you were required to file Form 8606 each year that you made a nondeductible traditional IRA contribution and it's Form 8606 on which you'll report the Roth conversion and calculate the taxable amount of the conversion based on your $60,000 of basis in nondeductible traditional IRA contributions and your year-end value in traditional IRAs.
If you failed to file the required Form 8606 each year, you'll need to correct that by filing these forms late. Line 14 of each year's Form 8606 carries forward to line 2 of the next year's Form 8606.
