Hugh to answer the windshield question look at pic 3 above. That is the Pink Lady and working from front to back both boats have a swept trailing edge but the PL sweeps back from bottom to top with the top being the longest point. Now scroll up to pic 1. That is the School Bus, the 89 backup boat. The windshield sweeps back from top to bottom with the bottom being the longest point.
Now to answer the Dumas question...I can only assume that they were trying to duplicate the the 1989 Circus. Because as HJ stated it is really a melding of the PL and the SB. It has the shorter nose and inset transom of the PL but the sponsons of the SB. There are some more but those are the big ones. In 1988 both hulls had the pointier sponsons. The Pink Lady was the U-31 Circus and the School Bus was the U-00 Miller and for one race the U-00 Circus. It's a confusing story but I won't go into all that now. Before the 1989 season the PL was refitted with radiused or rounded sponsons but the SB did not. They kept it as is basically and just repaired the damage from the flip in San Diego in 88. Both boats were painted identically in 1989 and there was one small decal on the nose of the SB that is not on the PL. Now as far as the Dumas decals are concerned they are actually a combination of 88, 89, and 90. The real story of the boats is somewhat confusing so it's not surprising that Dumas is a little off on accuracy. The Dumas Circus is fine as a fun boat and I'm sure that is what their intention was when they started offering it. As far as 1/8 Scale Unlimited racing is concerned, it would need some modifications to meet the rules of either racing organization. I've seen some Dumas boats that have had mods made and ran well.
Now for the paint differences between 89-90 on the PL. It's really very subtle. The pink that is at the top edge of the sponson where it meets the airtrap...on the 89 ot rolls over that edge and then stops on the inside wall of the trap well above the canard wing. You can kind of see it in pic 3. On the 90 the pink goes all the way down below the canard wing. Also on the vertical wings they had one that was longer than the other and extended above the horizontal. Plus they had a U31 decal on the right vertical at the bottom. That is one of the decals included in the Dumas set. I sent a bunch of these pictures to Shann last week. I'll try to post them later.