Rory
Your best bet for an economic revival of this car would be getting a factory B20B manifold with twin SU HIF6 or Stromberg 175 CD 2SE carbs.
Downdraught Webers on these cars are absolute crap.
If you wanted to keep in as an injected engine, going with something like MS3 would be the way I'd suggest you go. That way, you can re-use the inlet manifold, but would need to fit electronic injectors, etc. From a non-expert's POV, the finished product will look reasonably stock standard.
Remember that the K-Jet parts for these cars are now 50 years old. Many are NLA and what is available is very expensive.
If you do decide to restore the K-Jet, you'll need a new 5 Bar fuel pump - either now or later. I'd also consider replacing the fuel tank with one from a 1978+ fuel injection 240, which has an inbuilt swirl pot and lift pump.
The 1974 B20E head is a very good casting, with slightly better flowing intake ports from factory than the previous castings. A little bit of head work will get very good results.
Unless you're replacing the BW35 auto transmission with an M41 4+OD box, I wouldn't bother - the 4-speed M40 with 1:1 top runs at about 3600 RPM at highway speed. Only thing about doing an M41 replacement is you'll need not only the manual pedal box, but the correct gearbox crossmember, which is different to BW25 or M40. If I wanted to keep it auto, I'd fit an AW71 with an upright adapter ring*** - that way, I'd have an overdriven top gear.
FWIW, I have a 1974 145 K-Jet project, which unfortunately hasn't progressed very far as yet.
https://ozvolvo.org/d/2938-2938
It's also K-Jet, and it starts and runs, but there's a lot of rust to take care of before it's ready for roadworthy.
*** Yes; I have a vested interest there - I'm presently arranging to get a run of AW70/71/72 upright adapter rings made here in OZ. Details soon, but hope to make an announcement in about 3 weeks as to price and availability.
