Or, take the Silkair flight at 7am-ish, it will get you to SIN roughly an hour earlier (with no delay), at around 8am. If it's on a MH ticket (look on MH's website), then you may be able to talk them into interlining between the two tickets, though then you will only be able to check-in at KUL transit desk.

Immigration at KUL is very easy that early in the morning (and J passengers already have a separate line), but a pain waiting for check-in to open at 6-ish.

You should be able to use the Golden Lounge even as an arriving J passenger (if you can interline the bags), so that should help on that front. I don't know if they will give OWE benefits if you take the Silkair flight via a MH-purchased ticket, might be useful to check on that.

Note the standard risk of separate tickets, but ~3.5hrs should give enough of a buffer.