I think a fair guess would be MF was conceived first, for this reason:
On "Making a coaster" they said that Nagashima decided to go with Morgan after riding Mamba....so the start of design/engineering had to have been after April 1998.
CP confirmed that MF track was delivered to CP starting in December 98. If (some) track was manufactured and shipped that means all the surveying, designing, planning must have been darn near done if not done, and that would probably have meant the start date for MF was before April 98.
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- Peabody