OK woody, the whole rear axle assembly from the series 3 Bluebird is not really a good idea because of the width. If the rear end is from a sedan, then it has a totally diferent type of suspension, & removing all of the extra suspension bits, neatly, is more work than i want to do.
The diff is the thing in the middle

The series 3 gearbox is quite a bit longer than the 1200 box & it will require the removal of the original gearbox mounting brackets, & the fabrication of a new mount, further back. This is one reason why the stumpy gearbox is prefered for these swaps.

The series 3 car used a CA20 engine, with it's own bell housing bolt pattern while the L series had a completely diferent pattern. The gearbox itself is the same, but the bellhousings are diferent, so they will not bolt together.

What's the obsession with the H190 diff?

The original H165 will handle just about anything that you would be fitting into this car in the forseeable future. The H165 is available in a fairly wide range of ratio's, they are reasonably common, & are reasonably cheap to buy. The 3.9 to 1 ratio from Bluebirds & Stanzas is likely to be the best bet for road use.

While i think of it, from memory, the series 1 & 2 Bluebird wagon with four speed manual trans were the ones that got the H190 diff. All others in these two models got the H165 diff. I have no info whatsoever on the series # car, but i expect them to be the same.

This correctly sized, original rear end will also offer you a wider range of choices when it comes to wheel selection, so unless you are racing,... the H190 rear axle is likely to be far more drama than it's worth.
You may have noticed that Bluebird rear end swaps are not high on the agenda for 1200 owners. There's a good reason for that.

It sounds like you are clutching at straws here by trying to fit whatever it is that you have, or can get cheaply. It's far better to think about what is right for the job, then save up, & get it.

Think twice, or in your case, thrice, [under advisement] then act once