The Rover V8

[MikeB]

In the MGB I believe the engine weights weren't that different betwen v8 an in line 4, a bit more on the v8 but not enough to mess up the handling.
Go for it, I wouldn't put an old auto box in though, I would almost guarantee you'll love the dropping a cog to overtake and the ability to hold the power round the corners etc.

You'll have a load of torque anyway so you won't need to constantly change gear with a manual, horses for courses though..