the Vauxhall would be good as the diesel gearboxes give proper ratios.
They don't though, the F15WR that everybody recommends isn't great due to the wide ratio. The ratios in the F15CR and F10CR aren't great either.
I reckon I'm in a reasonable position to answer the original question. I've just ripped my Allspeed small block Vauxhall conversion out of my '71.
It fitted in a standard roundnose (with inner wings intact....mostly), it retained the exact look and feel of a standard Mini. The all up weight was very, very similar to a standard A-series engine. The balance of the car felt similar. The power was great, the gearing was as best as I could find with my limited internet research, but I was just always thinking "wouldn't a fast A-series be fun"
So I ripped the modded C16XE out. Now I'm building a 1330 A-Series, with a remote box. Nothing too lairy, a homebrew build, 10:1 CR, probably a 276 or similar cam, electronic dizzy, cross pin diff, 3.44:1 FD ratio, 10" wheels (I even kept them on the Vauxhall engine). It just feels like I was ruining the heritage of the car, so I am desperate to get it back to A-Series and enjoy it again.
I would love to go supercharged, but not yet. I want to get the car right before I go mad with modifying it.