They will fit but this is a bad conversion. The 205 tire is 1.14" larger in diameter. This will cause you speedometer to read 57.3 mph at a true 60 mph. This will also effect the handling and stopping distance of the vehicle in a negative way. Stick with the OEM size tire.
The Original equipment size is P205/70R15 95S
P215/70R15 or P205/70R15 will work as well
P205/70R15
P205/70R15
P205/70R15
P205/70r15 95s
My 2000 CR-V has P205/70R15.
4 cyl: P185/70R14 V6: P205/60R15
P205/70R15 comes standard on the LS model for that year. P225/60VR16 is standard on the XR7.
That's a much smaller tire, you may want to think very carefully about that. I certainly would not.
You should not have any problems at all. The size difference is minimal. To set your mind at ease, just contact a local dealership and ask for the Parts / Service dept. They will know the answer for sure.
The proper tire size for a 1998 Pontiac Transport is P205/70R15. This info is on a sticker placed on the driver's door jam.