the coupes have the H145 or 150 diff? (or something like that) Anyway, it won't get you out of the driveway with an L series!

Get the 120Y sedan BorgWarner diff. The same unit was installed in many larger local cars and will take quite a bit of punishment even with a worked L series.

Stanza struts will bolt onto the 180B control arms. But get some lowered heavy duty springs for them.

I'd be very surprised if an A14 rad (what is it out of?) will cope. I use a Volvo 244DL rad which was the perfect height for the 1200, but you could measure up a 180B/200B/Stanza or similar radiator. Just get the tape measure out and spend 1/2 an hour at your local wrecking yard.