So you want to install an L-series in your B-210/120y? Here is how I did it.

tools you will need in addition to your tool kit:
engine hoist
jack stands creeper
sawzall or cut-off tool
drill
floor jack


What you will need:
1969-73 510/1600 front crossmember
1969-73 510/1600 radiator and hoses grab the 510 heater hoses too
1969-73 510 clutch line
B210/210y automatic or GX driveshaft
L-16 to L/Z-22 engine
280z 5 speed
1969-73 510/1600 transmission mount
4 large fender washers to match the trans mount bolts
4 nuts to match the trans mount bolts
custom made exhaust 2 inch or bigger

OK now that we have our parts lets get started...
1. remove everything associated with the A-series engine.
2. now that all that is out it's time to swap the crossmember
a mark the holes that the crossmember are bolted to
b unbolt all suspension pieces from crossmember
c unbolt crossmember ( you will notice there are 6 holes for the crossmember)
d bolt in the 510/1600 crossmember using the holes that you marked
e reinstall all suspension pieces
3. now that you have the crossmember done cut the bumpout for the radiator out this is best done from the front
4. mock up the radiator and mark for the bolt holes
a drill holes to mount the radiator
b set radiator aside
5. Bolt together the engine and trans including clutch and assundries
6. swap out the clutch line and secure as you see fit ( I installed the clip from a Z)
7. cut the tunnel 4.5 inches back from the origional shifter location.
8. slide in your engine and transmission
a use your floor jack to lift the trans into position
b bolt on the stock crossmember mark the floorpan to match the crossmember
c drill holes to match the crossmember
d using the fender washers bolt in the trans crossmember
9. install driveshaft
10. wire up ignition and sensors add wire as needed
11. install radiator and hook up hoses
12. hook up fuel lines
13. fill all fluids (don't forget the transmission)
14. fire it up

NOTE: with the added weight you will need better brakes and stronger springs because this set up is a lot heavier and more powerful than the A-series you just pulled out.