I am trying to figure out the variations in the brake hoses.

Logically, there would be a different hose for the cars with front disc brake than for the cars with front drum brake.

Also, logically, there would be a different rear brake hose for the cars with swing arm rear suspension than for cars with the rear solid beam axle and leaf springs (Bellett B). Because the hose links from the chassis to the moving rear suspension, and the rear suspension layout is different for those.

But I have seen a vague Japanese mention that the there was a "early style" and "late style" brake hose for the Bellett GT. I can not remember if it was the front or rear brake hose. And there was no mention of when this transition was made.

Anyone have any more details on this? I am trying to make my search for hoses a little less confusing.

I got a response with some, but not all, of the clarifying information.

It looks like the rear hoses are the same for all sedans and GTs, except the Bellett B.

For front hoses:
The early type is 1964-65 Bellett GT.
The late type is 1966-74 Bellett GT and GT-R.
The Dunlop brake was mentioned as the difference for the later ones. This seems to imply that the early GT had a different front brake caliper. Need more details about this.

There was no mention of the sedan drum brake front hose.

OK, I have what may be a pretty good mystery going.

In my search for brake overhaul parts, I spotted a Japanese auction for front brake hoses, and had a friend pick them up for me. They arrived. The auction listing is long gone, expired from the website. But it said these hoses fit Bellett 1600 GT-R, and seemed to be saying they were the late version. There was some reference about the length or mention of a long type and short type. It has been way too long ago to remember the details exactly.

They are:
PN 5-09364031-0
The label has the GM (General Motors) emblem. So these were within the Isuzu parts distribution system between 1990 and 2008.

BUT, they are 340 mm in overall length.
Meanwhile, the 1969 GT hoses seem to be 455 mm in overall length.

The next detail really screws things up.
These shorter hoses have fittings with 10 mm x 1.00 pitch thread. This is on the chassis end and on the caliper end.
The longer 1969 GT hoses have fittings with 10 mm x 1.25 pitch thread. This is on the chassis end and on the caliper end for the Dunlop/Sumitomo calipers.
This 10 mm x 1.25 pitch thread is what has been screwing things up for me all along, because the chassis end of the front hoses and both ends of the rear hoses are not made in this thread size.

Now for the mystery.
I think PN 5-09364031-0 is the 1964-65 front hose.
The next question is the thread pitch on the rear hose for the 1964-65 cars. If it is consistent with the front hose, it will also be 10 mm x 1.00 pitch thread.
Can anyone confirm this?