Not a fan of wood as it can move according to atmospheric conditions.
Dar better to have a steel sheet, at least 3mm thick on top.
Even better, make the entire bench from steel; substantial angle iron, or box section for the legs
The objectiive is a rigid bench.
Once the lathe is on the stable bench, then is the time to check for, and eliminate twist from the bed. A lathe with a twisted bed will never cut parallel.
Ian Bradley describes how to do this in “The Amateur’s Workshop” and “The Myford 7 Series Manual”
Somes known as “Rollie’s Dad’s Method”
Strangley, Sparey doesn’t!
Howard