Spinal Mounts

I played FT last night, and EFSB a couple of weeks ago, which got me
thinking 
about Spinal mounts ala Traveller.  I am starting to think along the
lines of 
the Beam weapons in EFSB, or high number FB Beam batteries.  My first
take is 
20% of total mass and cost 3xMass used and only allowed the Front arc.. 
Effect 
is 1 die per mass as Beams or ?  My goal is to make them cost effective
only on 
the larger ships i.e. mass 100+.

Thoughts? Flames?

Michael Brown