However, i'm thinking that this should be a little lighter, like a miniature version of the gunboat. Light enough for small police factions or permits, but heavy enough to give people a run for their money.
Having a forward cannon would classify this under another class, more towards "battlecruiser" than super heavy fighter.
As for the engine, ya, keep it small so that it can't fire excessivly huge things. Smallerish, if that makes sence.
If we were to put a forward gun on it, i think that it should be more of a hull killer than a shield killer. Not much d/mg on the shield so much, as to keep it line with what the idea would 'go with'.
Personally, i'd love to have battlecruisers. But it would involve a lot more work for all the houses.