I see now. Looks like I'm the one who needed some clarification, Ross.
Could you PM me a link of where you went to obtain this information on 290's infancy, Tiger? I distinctly remember a divided highway after Mangum, and I want to say it ran clear up to Cypress. After Cypress, the median went away and that old section of 290 (now business 290) is what it became afterwards. 290 in Houston, as I recall, was built in the median directly between the two double lane roads around 1981, maybe 1982. Now, I'm a little nuts, but I don't think I've taken the dive off into the deep end of crazy yet. My folks used this route to get to my grandparent's place in Bellville, and this would have been in the 70s. I didn't start taking the I-10 to Texas 36 route to get to granddaddy's until I was driving myself in the mid 80s.
Gracias, mi amigo.
Edit to add: Never mind, I see you linked the map in your post above. Have you ever found anything further on the more northern portions of the Northwest, between 8 and 34th? I know you have become quite the encyclopedia of knowledge on that particular highway since the construction began.
In 1967, the interchange would've already been built but would've just terminated at the frontage roads and ended at Mangum (as of January 1965), much like 225 and 610 today. Big interchange...quickly goes to frontage roads...ends at another road and not at a right angle. The highway between Mangum and Beltway 8 didn't exist, but the frontage roads from roughly where Beltway 8 is (and beyond) had been upgraded to a divided highway with a large median, because planners had predicted that urbanization would come fast and quick to Northwest Houston. It really didn't...there was plenty of activity along Interstate 10 heading west out of town toward Katy, but even in the late 1990s and early 2000s, it still felt that you didn't really reach the "Houston" area until around FM 1960. (This is of course, no longer true.)
If the platting map is correct, Brookhollow of Houston had it replatted to its current state before selling it to Humble. I just remembered that despite my scan of Houston Today I got from another source is quite garbage when it comes to the Brookhollow map unfortunately but I did remember to take a picture of the page with my phone, seen here. The striped area is the hotel (Sheraton, but a Marriott in the 1980s), and that seems to confirm that maybe what happened is that Brookhollow bought the land, and redrew the plats to the future tenants of the business park, which were then actually sold to them.