When installing MGB clutch with the MGA 1600 type gearbox, You may find a small bit of interference inside the bellhousing near the starter position. Note the area circled in red in picture at right, and marked in red in picture below. The fix requires grinding a bit of metal from the bellhousing, which may involve several fittings of gearbox to engine to check the fit. But there is an easier way.

On August 02, 2013 Eric Russell in Mebane, North Carolina, USA wrote:
"Rather than R&R the transmission innumerable times to check the progress of my efforts to grind away enough material to fit the clutch, I made a simple jig from a scrap piece of 1/2" plywood. I calculated that the clutch cover interfered at 5" radius by 2-1/4" deep (from the transmission to engine back plate surface). I made the jig 5-1/8" radius and set it 2-3/8" deep into the bellhousing. I slipped the jig over the first motion shaft to gauge how much material to remove and where. I put a hose clamp onto the first motion shaft so that the jig would go on at approximately the right depth as calculated above. Once I had it close to fitting well, I put a little paint on the end of the jig and slid it into place. The wet paint would then transfer to the inside of the bellhousing showing where I needed to remove a little bit more material".