At 06:43 PM 11/9/03 -0800, Barrie Robinson wrote:
"To all those challenged in installing their heater box in an MGB I have got an answer ...”. And he sent photos and notes, which are posted at the bottom of the web page here:
www.chicagolandmgclub.com/photos/b_heater

Then consulting the Haynes manual Barney Gaylord found this:
For the early models: "Lift out the heater assembly". "Take care to re-route the air control cable correctly".
For the later models (GHN5 and HGD5 models from vehicle No 410002), (That would be the start of the 1977 model year in June 1976): ".... withdraw the heater unit from the car". "Feed the temperature control cable through the bulkhead slot before fitting the heater unit".
This sounds like the factory must have wised up after a while and added a slot in the 1977 and later models, similar to the cut shown in Barrie's picture. If this is the case, then it would be nice if someone with a later model car (hopefully with the heater already out) could take a picture and measurements of the "bulkhead slot" to show the factory configuration, and this could be used as a guide for modifying earlier cars.

At 12:42 PM 11/10/03 -0600, Chuck Renner wrote:
“.... I can take a shot of the arrangement in my '79.”
We now have a nice resolution to a sticky problem and a few more footnotes for installing the MGB heater box. After 14 years of production, the MGB body stamping was changed for the 1977 model year (June 1976). Better late than never?

Chuck Renner has sent some pictures of the heater well area on his 1979 MGB to show the differences. After June 1976 there is a large slot in the bulkhead for passage of the heater control cable. These pictures show where the slot can be cut in earlier cars to make the heater installation MUCH easier. See photos and updated notes here:
www.chicagolandmgclub.com/photos/b_heater
Scroll to the bottom of the page for the recent photos and notes.

You may also notice a deep indent in the bulkhead for the post-1976 MGB which should allow easier compression of the thick rubber gasket pad during installation. This doesn't help with the earlier cars, but Barrie Robinson assures me that the heater went into his earlier MGB a lot easier just by cutting the cable clearance slot in the bulkhead. That modification is shown one step higher on the same web page. And yes, I suppose the KY Jelly would help too (as long as you can explain to your S.O. why you carry that stuff in your toolbox).