Scart carries a single composite sync which is used for RGB. VGA carries separate horizontal and vertical sync signals.
When going from VGA to Scart, you could combine the two syncs from VGA into a composite sync using some TTL gates. But I don't know of a way to split the separate horizontal and vertical syncs out of a composite to go from Scart to VGA.
But, your projector may work with just the HSYNC. It depends on the spec of your projector.
See the link. At the bottom of the page, it mentions VGA connections.
http://www.epanorama.net/documents/vga2rgb/scart.html