Jim, Greg & the list.
Masi from time to time built .5 sized bikes, this is not unprecedented.
This seller found the bike in a dumpster, as he describes elsewhere.
An experienced viewer of the images can assess it probably better than the seller.
As to why the replacement fork? Make an educated guess.
Unusual BB cut outs, major restor job required. And then one will only be able to date it very approximately.
John Jorgensen
Torrance Ca
"Masi Beach"