Seems to me a much cheaper alternative would be to either build some more OV-10 Broncos (twin turboprop used in Vietnam as a FAC aircraft) or just use A-10 Warthogs. Both can go low and slow and especially the A-10 can lay down some withering close support hell from above.
Back either of those up with an AC-130 gunship and the V-22s might even have enough time to descend at a rate that won't get 'em into VRS
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Dave Blevins