Jeff your not dumb. 88 was a very confusing year for those boats. It took me a while to get the whole story. The 88 was smooth and no vent when it was all pink. Both the Miller and the Circus had rear vent with a vertical vane down the center for the last two races. In fact there was a weird bonnet that they had that attached over that vent that extended back almost to the back of the fairing where it meets the turbine tube. They built those to protect against salt water ingestion. There was also an airdam that they could control from the cockpit to close off the the airscoop while getting on plane. The U-00 (blue sided) Circus ran with that bonnet while testing but it was not on during the race when it flipped. The Miller which had a string of DNS's all day at San Diego did run, or try to, with it on which covered that vent. It ran with it off and won in Vegas which was the following race.
In 1989 both boats became Circus boats with identical paint jobs but they made the rear vent larger and put in a flat section all the way from the vent to the end of the fairing on the 8700 boat. You're right though the airscoop was pushed back farther off the back of the cockpit and it was shorter on the back end as well in 89. They also radiused the sponsons on that boat but not the older 8401 hull. It kept the same cowl from 88. On that boat the airscoop was up further and the back was longer with the same vent as in 88. It had the flat transom with small supports under the verts. There's good shot of that on the Miller 0032. It had the longer nose but the paint jobs were identical. In fact Chip won Seafair with that boat, which was known as the School Bus, because he broke the newer boat twice that year.
Trust me 88 was such a wierd year for those two boats. Lots of stuff changed. If you look as all of pics from the open cockpit Miller...the decals changed, mainly in size and some placement. It also was repainted after a fire and the paint patterns and striping changed slightly too. The HIGH LIFE lettering changed from one boat to the other too. Miller was frustrated with all of the problems all season and pulled the sponsorship at the end of the 88 season and Fran Muncey sold the team to Bill Bennett from Circus Hotels for the 89-90 seasons.
The 8401 was eventually sold to Jones racing and you see that same long nose on the 91 American Spirit and the '93 Circus backup hull.
Anytime you need help shoot me a PM or an email. If I don't have the answer right off the top of my head I'll find it for you.