Vincent Audio SV-236 Mk II

Just got this amp and intended to replace the stock tubes right away, after reading about how doing so can improve the already-great sound.

Does anyone know how to remove the top plate of this amp to get at the tubes? There's a series of screws on top, but they're not Phillips head or Allen key screw heads.

Do I need a special tool to open this thing up to get at the tubes?