They pretty much bolt on, most manifolds use the dowel pins that stick out of the B20E/F head for the Injection intake to produce perfect alignment.

The new 45DCOE's that are around for purchase these days have 36mm chokes, 4.5 Aux Venturi & F16 Emulsion tubes. You can make these parts work fine on a Stock B20E/F and when you upgrade the head & cam, move up to 38, 39 or 40 mm Venturi's & tweak the jets to suit.

D-Jet injection works fine with D, K & Isky's VV-61 cams.

I would not leave D-Jet behind until you have a decent cylinder head and cam, which are hard to get. OR, if the D-Jet system needs an expensive part to fix it & you intend to increase performace over time. Having said that, 40DCOE & EARLY 40DHLA carbies found on Alfas up to 2Litre are OK if you can get them VERY CHEAP. On a 1750cc or 2000cc Alfa, they deliver 130BHP, same as a B20E.

If you have a B18, some porting on a B18 head with a VV-71 head might get you some more topend power via turning more RPMs, say 150BHP @ 7000rpm, but most B18's go to standard bore B20 easily & you know what they say about displacement...

With mild cams such as D, K, VV-71, some mild porting & a decent exhaust, a B20B with twin SU's in not a bad thing, automatic best MPG & performance ahead of a B20E. If you have an overdrive & like to tour. Twin SU's, and elongated engine pipe & 2.25" exhaust will go along way between gas stations while cruising @65 to 70 MPH.

The primary proplem with B20E/F D-Jet or K-Jet engines is the intake it too big & too short. It was designed too look good on a P1800E.