That's a clear answer, but wether the gearbox bolts on from the outside or from the inside doesn't mean the bolt pattern is different. Looking back at my picture, it looks like the M47 also bolts on from the inside, so maybe going to an M47 isn't that complicated if you already have a M45/46 bellhousing.

In a previous post I wrote that my M47+3.91 rear axle does 2750 rpm at 100 km/h in top gear, but today I found out it's much closer to 2500 rpm despite being on slightly smaller tyres compared to the factory original 185R14 setup (now Virgos on 195/65R15 which are about 2.7% smaller in diameter).

I know for a fact that the rear axle is 3.91:1 as that's what it says on the sticker on the axle. So either that's wrong (unlikely) or the tachometer is showing the wrong rpm at that speed (yet at idle shows a correct 750 rpm).