When the speedo cable on my BN7 failed, I found that the PO had trapped it behind the metal shield that fills the gap between the firewall and transmission cover. That meant doing a lot of disassembly, not helped by the fact that I have a Toyota gear box. This required me to attach the Toyota drive fitting on a new Healey cable at the transmission. In refitting the new cable and housing, I chose to drill a hole in the top left of the tranny housing at about 11 a.m.--toward the pedal side--finding that the carpeting nicely covers it. Next time I will just pull back the carpet and draw the cable housing out. Given the challenge of making the Healey/Toyota drive cable, I hope that won't be soon.