The good thing about fuel injection, is that once you get it up and running, its reliable and doesn't need any fiddling, that is what always bugs me about carbs and points. Your other option could be an XK engine on carbs as used in the XJ6 until 1984, more costly though. There is also more unusual sixes such as the Rover 2600 from the SD1 or the 3Litre used in Rover P5s, both of those run on carbs. You need a larger capacity unit, that's why I was thinking Jaguar as they are generally around the 4 Litre mark.
Considering linkages for gear change and clutch, an auto just seamed a simpler solution. The Matilda 1 (Runner) at the Tank Museum has an SD1 3.5 Rover V8 and SD1 Autobox installed.
https://youtu.be/FQI2P1485fQ