AHC: Keep Liberia (relatively) prosperous

Your mission is to preserve the economic growth that Liberia enjoyed during the 50s, 60s, and 70s. You should also prevent the civil wars that wracked the country. Bonus points if by 2014 Liberia is stable and democratic. Is this possible? Can it be done even after Samuel Doe's coup? Or does the Americo-Liberian oligarchy have to be forced to gradually, hand over power to the rest of the country, instead of losing out all of a sudden in a coup?
I think gradual hand over, or a movement like America's Civil Rights movement, would be best to keep growth and stability.

Don't think either option is realistic though, given how badly the Americo-Liberians were outnumbered and how brutal they were.
I think the last best chance for Liberia to have avoid it's tragic history would be for the 1979 Rice Riots to have led to the impeachment of William Tolbert and for the True Whig Party to recognize how perilous their hold on power was and I enter a partnership with the progressive alliance in an attempt to mitigate the damage done by the riots. From alladrica.com:

It can be recalled that in early April 1979, former President William R. Tolbert's minister of agriculture, Florence Chenoweth, proposed an increase in the subsidized price of rice from $22 per 100-pound bag to $26. Chenoweth asserted that the increase would serve as an added inducement for rice farmers to continue farming instead of abandoning their farms for jobs in the cities or on the rubber plantations.

However, political opponents criticized the proposal as self-serving; pointing out that Chenoweth and the Tolbert family operated large rice farms and would therefore realize a tidy profit from the proposed price increase.

The Progressive Alliance of Liberia called for a peaceful demonstration in Monrovia to protest the proposed price increase. On April 14 about 2,000 activists began what was planned as a peaceful march on the Executive Mansion.

However, the protest march swelled dramatically when the protesters were joined en route by more than 10,000 "back street boys" causing the march to quickly degenerate into a disorderly mob of riot and destruction. Widespread looting ensued with damage to private property estimated at over $40 million. Tolbert's credibility was severely damaged by the rice riots.

So perhaps have the riots lead to the fall of Tolbert and for VP Warner attempt to enter a partnership with the PA.