Looking at the Wiki Im wondering if there is a way to use the gears from
another manufacturers gearbox, one from a bigger box and shaved/modded
as well as off the shelf gears that might be left over as NOS from the
early 3 speed gearbox?

# 3-speed R3W56L steering column shift
1st - 3.380 , 2nd - 1.734 , 3rd - 1.000 (Rev - 3.640)

# 4-speed F4W56L floor shift
1st - 3.757 , 2nd - 2.169 , 3rd - 1.404 , 4th - 1.000 (Rev - 3.640)

Looking at the above youd want the
1st - 3.380 , 2nd - 1.734 , 3rd - 1.000 (from 3 speed)
then 4th gear some kind of overdrive from something else
or at worst someone to make a number of 0.7- 0.75 gears.

This would make all those a14/15 engines in lightweight
datsuns be a joy to live with a 3.7 or 3.9 rear
BIG PROBLEM IS STRENGTH - every gear/shaft/parts
would need modern case hardening!!!

Any input guys?

Should be possible. Dan Hall made several 5-speeds out of the 4-speed. And PJZ was trying to sell them.

id say it would make A series 1200s an arse to drive with a 3.7 or 3.9 rear end. imagine the gaps between gears especially with a lack of torque

This has been done on the chrysler a883 (or was it 833, forgive me) box. they are/were a VERY heavy duty box, good enough behind hemi v8s (and the internals are so big you can pass ford toploader GEARS through the inside of the 883 synchro rings!)

Anyhoo, for models behind some slant sixes, what they did was fit a new laygear and new 1/2/3rd gear. 4th (in the box) was still technically 1:1, but the first and 2nd gear ratios were spread more, to make it like a 3sp manual. where 3rd was, they reversed the tooth count so that it actually became an overdrive gear when in third. these boxes used external linkages so they simply flipped the front external lever for 3/4 upside down, and when the shifter selected 3rd it would actually be selecting 4th and vice versa, so they shifted like a conventional 4 speed, but not with a wider ratio spread and overdrive top. they ended up not making the gears out of such strong material, so they aren't typically used by anyone, they all go for the 'original' and heavier cased hemi/other mopar v8/variant....

Even if you could do a similar job, it'd only be remotely close to financially reasonable if you happened to have all the tooling/machinery required for the job. Even if you did that, one would surely still have to make a case for either the toyota t50 conversion kit, or alternatively applying the same skills to the bluebird 5 speeds, and grafting on a bellhousing to adapt them to use on an a12 or any other a series.

When I look at the datsun ratios for the A series and using them everyday with a 3.9
rear, I must say it is an arse of a box already. First is non existant and only 2nd
and 4th are worthwhile.
Ive seen many variants on the T50 series boxes and wondering if the 4 speed boxes
could be used with the following ratios

# 4-speed F4W56L floor shift
1st - 3.380* , 2nd - 2.169 , 3rd - 1.000* , 4th - .75

only 1st and second would come from a 3 speed and the 4th either custom made (big bucks)
or a modded gear from another box?

When you go from an A10/12 to an A14/15 the gap between 2nd and 3rd shouldnt be an issue.