Hi again, I took a couple of pictures of the heater hoses on my car. You can see them at:
http://home.mindspri...sideHoses01.jpgand
http://home.mindspri...gineHoses01.jpgThe inside picture shows the recess that should be behind your pedal box. This recess should be mirrored on the left side of your passenger compartment. The engine picture shows a top down view of the hoses passing through the plate where my top engine steady is. You'll notice the grommits. I enlarged the holes and added those. Originally BMC/BL did not use anything to seal those openings or to protect the heater hoses from the sheet metal.
Don't worry about what length your existing hoses are. Heater hoses are relatively cheap. Buy bulk material and make them whatever length is right for your application. As for the holes and where to make them, you really need pictures from a right-hand drive car and I can't help you there. However, if they mirrored the hole pass-through points on the LH and RH cars, you should have a filler plate where my clutch and brake masters are. Chances are you'll have holes under the plate and through the body at that location. If not, it won't be hard to add them. However, I suggest you look up "step drill" and buy one of those tools to drill large holes in sheet metal like this.
I'm not sure I followed your question about the demister vents. You'll need to spell that one out a little better for me and explain what your concerns are. As for taking pictures of that for you... I'll see what pictures I already have but I'm not going to take my dash cards out to photograph what's behind them. It's just too much work with too great a risk of damage on a Mk1.