I'm partial to using small twist latches if I'm replacing. They're solid, low-profile, and inconspicuous when the cover is off. When the cover's on, they hold tight and don't come unlatched. I'd be tempted to keep the originals, but only 2 of the original 4 are there. I have not seen any repros that are an exact match to the originals (or, at least what's original on this particular piano), so I don't see the point in replacing impractical original latches with impractical new latches that don't match the originals anyway. To each his own, though.
The former owner came up with the original preamp, believe it or not.
The existing baffle is cut differently than the one in the photos on this thread. It has a large rectangular cutout between the speaker holes.
Ray- I wouldn't recommend going to two latches unless you also use the heavy-duty hinge. Also, with two latches (or loose latches), more force is exerted on the back panel of the piano case, which makes the joints prone to separating. The sparkletops used solid softwood with finger joints, so the joint is stronger than the early Mk1's without corner reinforcements, but by no means indestructible.