There are a few things we can be fairly sure about - the cloak is not a good one, judging by how well we could see it compared to the cloak Kirks Bird of prey had in ST IV - a design now well over 80 years old. The ship doesn't seem to be part of an existing class, since Picard and Data didn't know what it was for until they got inside. That means it was almost certainly built by the conpirators - it could have been refitted from an existing cargo-type craft, but if so you would expect Data to have mentioned this when he first saw it. Given its role it's probably unarmed, and is probably a no-frills design whcih was intended for this specific job and no other.

The sizes and size comparison image come from Star Trek : The Magazine. All other data is speculative, and intended to support the facts and inferences given above.