Welcome to the site and congratulations on purchasing.

I believe this batch was new to Sunderland Busways, but continued with Stagecoach following the takeover. There's a couple photos on Flickr of H670BNL working in service for Stagecoach in Teesside:

Stagecoach - 14670 - H670BNL - StagecoachNE20040264 by Gary Mitchelhill, on Flickr

Here's H671BNL (671) with Busways:

671 H671 BNL Sunderland Busways by North East Malarkey, on Flickr

I think it was 14669/70/71/73/74 that were converted to sightseeing buses, remaining in the North East. H669BNL was then preserved by the North East Bus Preservation Trust (NEBPT):

JPT906T and H669BNL by C522LJR, on Flickr