After installation of the Moss air conditioning kit in my 74.5 MGB GT, I decided I didn't like the vents that were supplied with the kit. After doing some searching, and with clues from other members, I ordered the vents for the side from Nostalgic Air and the adapters to provide AC air from the center dash fresh air vents.
Installing the side vents which match the curvature of the dash was quite easy.
To install the adapters for the center fresh air ducts was puzzling. I couldn't see how to remove the grills from the dash. Finally I discovered a tab on each side of the lower portion of the adjustable vents.
With a putty knife and a box cutter I was able to put the putty knife under the inner grill bottom and while prying on the tab on each side and putting pressure on the putty knife the bottom of the grill popped out. Then using the putty knife around the edges and prying, the grill came out.
I pulled each one out as far as I could and removed the flexible hose connected to the cowl vent box.
In order to remove the flexible vent hose I removed the glove box which is fairly straight forward in it self.
The adapters that Nostalgic Air supplies have a fairly short A/C vent hose connection point so I drilled the hose and adapter an put upholstery screws in the top and bottom to hold in place.
I taped up the holes from the fresh air box to keep air from coming in (I hope it holds!)
I then slipped the A/C adapter with the hose attached through the hole left by the glove box removal behind the driver side center vent and mated them together routing the hose down to the evaporator connection point. I repeated this of the passenger side center vent. Connect the hoses to the evaporator and enjoy!