Advice needed - connecting the centre beam

Can anyone offer some advice about connecting the centre beam to the forward and aft beams. That is, “L brackets” or “plug” methods (both mentioned in the plans) versus other methods; pop rivets versus bolts; the need (or not) to be able to remove the centre beam. All suggestions welcomed, thanks,

A plug at one end looks neater but isn't essential. "L" brackets work.

Rivet the "L" brackets to the beam with aluminium rivets and put a bolt through the centrebeam so it can be removed easily.

Hi Tim,
Thanks for that - greatly appreciated,