We blue print bore a lot of cam tunnels in the 010 blocks, Dart SHP, Darts, Bowtie as its a stronger core less twist and the bigger bearing can support more load.
BBC cam tunnel is very popular with guys using flat tappet cams as you can get a better lobe that will work with a 1.8 or 1.9 ratio rocker with out hurting the nose of the cam because its more rounded and has more surface area.
BBC journal is only .020 smaller then the 50MM cam core.
We are a WD for Dart