The key to the ignition on my '78 B has the plastic BL logo. So does the key to the glove box (only it is all metal with no plastic). The doors and bootlid use a much smaller blank.
The key to the ignition of my 74.5 B/GT is identical; the key to the doors/hatch the same blank style as the '78. I do not have a key for the glove box for that car. It had gone missing prior to my buying the car. What was interesting with the GT is that the spare key was still intact and obviously unused in the engine compartment! It, as I stated earlier, is the plastic key head with BL logo.
I only have one key that works the ignition, doors, and bootlid on both the '68 MGC and the '69 MGC. With the pillow dash, there is no glove box. They are all metal-only and the smallest of the three blanks described above.