Crossmembers are very different so are not interchangeable.
 
Datsun 1000 has a leaf spring running inside of it
 
You will have to excuse all the aluminum angle bolted to my 1000 crossmember, but here are 1000 and 1200 crossmembers side by side.
 
.

No problem.
 
Glad I could help.

I agree with D about flat plate being the way to mount late A engines onto early crossmembers.
 
I am not so wise and so...I am going completely and utterly overboard and modifying everything engine mounting to avoid the adapter look.

Part way through a 120y leaf spring bushing mount.
 
Still need to do some final shaping and remove mill scale before hopefully having my friend weld it up on the weekend.
 
Wanting a bushing mount with a square look to not look overley out of place in there.
 
Ill update my build diary with some more info on these once they are done.
 
  

What modification is required to get a L20b mounted in a 1k?

Assuming you can make it fit and can find an engineer to certify it, mods would include.
 
Engine and gearbox custom mounting.
Tunnel modification.
Custom drive shaft.
Diff upgrade.
Seatbelts.
Larger radiator.
Brake upgrade.
Exhaust.

If easy is your plan then A series is the go.
 
Just depends on your plans for the car.
What are you trying to achieve with the engine swap?
 
Best to have a clear goal in mind and work towards achiving your goal.

I wouldnt class a CA swap as easy.
 
But it has been done into 1000's before.
It certianly ticks the boxes for competitive track days, street car and avaliable parts.

You can run an L18 L series from an early 180b to avoid any pollution gear or cat converters
you send it to Baz at datsport he can arrange to get it C Sleeved for 90mm bores.
this will give 1985cc, you can get the NA20 cylinder head from Japan for the roller rockers
then a new cylinder head from China brand new which are better than Japanese combustion
chambers for higher performance (they are an updated design)
That is a SOCH crossflow head that is an update of the Z18et or z20 heads.
Run a stock Z18 or Z20 rocker cover and front timing case.
Run a tighe camshaft with 262-272 duration and 14mm lift, cheap flat top pistons for a Honda K series
R1 41mm quad bike carbs, custom headers or off the shelve Z24 ones fit.
Conrods are stock prepped L16 or get cheap H beams for 300aud.
You will have a 170hp 145lbs torque engine that weighs less than an L16 or L18.
Gearboxes are easy and roller rocker SOHC design is a thing of beauty.
 
The L series became the Z series then lastly the NA series.
The beauty of this is no pollution gear, easy build all fits, sohc with roller rockers,
big capacity but says 1770cc on the block or you could use an L16 with L18 crank.
To avoid issues with engineers, they will never know the bore size or sleeving.
Last of the NA20 engines had MLS type of metal head gaskets.
NA20 head is only 16.5kg (SR20de & ca18de are 24-26kg)
Sleeved and grouted L18 is about 38-40kg, ca18 bottom end is 42kg.
Either way lighte bike carbs also save 3kg of carb and manifold weight
The overall weight of the LNA20 would be 15kg lighter than a Ca18 & 200cc more.
https://ixquick-proxy.com/do/spg/show_picture.pl?l=english&rais=1&oiu=http%3A%2F%2Fimage.minitruckinweb.com%2Ff%2F9125297%2F0712mt_06_z%2B1997_nissan_d21%2Bengine_bay.jpg&sp=b56bd87aaf26bcb3dd7145a973108416
 
If you want to go crazier you need custom slipper 28mm pin height pistons and fit an L20b crank with L14 rods
you will get 2188cc and engineer will only think its 1770cc L18 engine block
 
 
If you dont mind modern, import a Honda V4 st1300 , sequential box modded electric starter diff for reveresing
https://www.youtube.com/watch?v=ZFzA39vlQ94