There are tons of 4-speed OD boxes in the UK!
You can also use a late-70's Getrag 5-speed stick.
The stock Series II Jaguar XJ automatic pedals box can be milled out, since it is the same box as the manual trans. It just needs the clutch pedal shaft machining.
The master clutch cylinder and pedals/rubber pads are the same as a Mark II.
The XJ Series I has split pedals boxes and are not as rigid as the larger base Series II box.

 

A cheap option if you can make a custom inlet manifold is a set of bike carbs, just have to run a wideband sensor to tune the idle and main jets which will be required to be changed to suit a 4.2litre.

I'm considering this in the future for my mk2, something very different yet when setup can be a great option, slide carbs can be mounted on a variety of angles which helps for size restraints.

 

I mounted a set of Mikuni 34mm flat slides(I took off a Suzuki GSX1100) on a mini 850. Cost a few pay packets but it was worth while. Don't know the details of what was done as I was single and had cash to pay to have it done.
But it improved the 850 mini no end. My parts guy(Stan) from my local Suzuki motorcycle dealer did the conversion in 1992. I still buy bike parts from him today at the local Triumph/Suzuki Dealer

Oliver?s Motorcycles Brisbane | New & Used Motorcycle Dealer

 

Some of the carbs are modular, like the Honda ones, so it would be easy to get two sets, delete one of the middle ones and run two sets of three carbs, simplifying linkages, or run all 6 joined but the issue there might be inlet port spacing

 

Three of these would be very amazing but the tricky bit would be the ECU.
The ECU likes to control pairs of injectors, not 3 of them.
These are equivalent to 1-1/4" SU carbs, so three of them would do the job.

Yet another An MGB Fuel Injection Manifold

 

My 16,000 miles XJ6 S1 has nasty bad running twin Zeniths. I'm in a similar dilemma.
I thought about trying to score a triple SU manifold from a 420 G but these cars are rare around these parts. May be the best option is to use Twin SU HD 8s.


What did you end up doing in the end?

 

Has anyone ever done a reproduction of the 420 manifold?


There is a large amount of cars that could use it

 

i have a modifyed su inlet manifold for twin webber 40/45/ 48s it was a proto type manifold my dad had made for his jag engine car i have taken it off and ready to sell now.
bike carbs are realy not a good option unless being fitted to a small engine car of a simeler size cc to the bike the carbs came from.
i have a friend with a mk2 escort with a 4cyl 2.0cc and a ford st 170 fuel injection engine that was 170 bhp standard. he bought it with bike carbs on it and it was only 147 bhp.
so it was less than standard.
he recently bought 2hand manifold a webber 48s and had another dyno this week and it was 186 bhp.
so bike are not all people make out to be.
I now have bought mk10 420 triple hd 8 2inch su carb set up to stay original for mine.

 

Tom,
twin SU 2" will work well, you can eliminate the AED (choke system) I converted mine to a manual choke setup -NOT SU style but cater/Stromberg style (can send pics & explanation on how i did it), blended my own oil for the dampers.....tom

 

Throwing bike carbs straight onto any engine without tuning is not the right way to do it, same with a set of webbers, or any carb for that matter, you change the jets to suit the motor.


Bike carbs will require a big step up in main jet size to suit the new engines fuel requirements, but the fact that they generally are a 40mm throttle size and usually a slide throttle, unlike a 45mm webber which requires chokes around 36-38mm.


I guarantee that focus motor if tuned properly with those carbs would have yielded a better result than they initially had, but the ease of the webbers, the support for them and the knowledge base out there compared to bike carbs makes total sense.

 

The last point is a very good one, naturally tuning is critical to any engne/carb marriage. There are certain US model Harley-Davidson motorcycles that as an upgrade, run an SU HS8 (2 inch) carburettor, such as you will find on home market S1 and S2 XJ's and as a consequence there are adaptors and multiple jetting options available for a direct-fit replacement Mikuni. I have the actual model of the Mikuni somewhere in my files and will have a dig around to find any relevant info for you Tom. As an aside, since I am in Australia, we have both SU and ZS equipped XJ cars and experience bears out that your desire to move away from ZS carbs is a wise one. Even if you were to simply move to twin Su with manual chokes fitted (as I have done myself) I am confident you will be happy with the improvements.