What about an overdrive unit from an M.G or Triumph?

Excellent ideas, thanks. I don't have any special knowledge about 6-speeds for A12s ... sorry to disappoint ...

Any chance that the Lexus is300 6-speed uses the same bell housing as the T50?

WTF!!!! Dd we here are hard enough trying for a 5 speed!!!

Yeah I know what it is you USA guys are sick of 63a and lesser 60a 5 speeds for 50 bucks on Ebay right?!!! while we kangaroo eating critters here fork out 3 times that for measly 4 speeds.

If youre serious then Miata or Eunos roadster as in Japan can be had for the price of a well sorted 1200 unless you go and buy one of a wrecker up there yourself or the triumph dolomite overdrive perhaps could be the go. personally Id rather fit a toyota 4 speed auto which has overdrive which has like a high and low on each speed electronically controlled the zaniest thing is how with it on my liteace van I can cruise in reverse the same as forward!!! with the same engine revs!! I had to back off after hitting 90 kmhr as I almost lost it.
Then run solenoid swiftches to your steering wheel a-la-F1. These gearboxes are awesome strong, flexible and compact.
You can also use a nissan 4 speed plush box but dont know anything bout them.

$50??? I wish. More like $150-200. Sure I want a 6-speed -- direct 1:1 fifth AND overdrive.

The is300 (Toyota 2JZ engine) 6-speed I heard is the same gearbox used in the MX-5 Miata, Nissan 200SX and Honda S2000. This is the same basic engine (2JZ) as in the Supra and ES300 I think.

Autospeed's Gearbox Swapping article

I have an electric overdrive in my MGB,and it gives me 6 gears. Adding one to another gearbox isn't that straight forward as the mainshaft is extra long to engage the hub in the centre of the overdrive unit. Though it would'nt be impossible....with a bit of planning and machining. Cutting back the extension housing and welding a mounting flange might be the go. Problem is though that even these old units still pull good money with the classic car boys, or should that be old boys !!

DId MGV8s come out with them too?

I love the v8 versions they really have some good times on the track only bettered by big dollar big power modern race cars. Pity they arent more affordable.

Ok boys...this has got me thinking... yes.. very dangerous indeed..

I'm now dreaming up designs for a 2 speed overdrive "extra" gearbox, that would fit behind a stock gearbox in the tunnel.

Would be an interesting option... Probably "a lot" easier to squeeze a factory 6 speed in the tunnel...

If you want a 1:1 fifth but six speed g/box why not stick with a Nissan S15 box???
They have those ratios + it is pure genuine Nissan/Datsun.
Just a thought
Jon

Pure Nissan? Even though the gearbox is made by Aisin and is also used by Honda?

Seriously though, this is from an SR20 engine, right? Would the bellhousing bolt up to, or be easy to modify, to fit the A-series?

They are on late S15 Silvia/200sx's, which usually come SR20DET powered. Accept your point re the (makers).

I've never seen one in the flesh, I must have a roam around the wreckers one day. I would say they wouldn't fit it a std 1200 trans tunnel and you'd have to custom make/bend one. Bolt up I doubt, but anything can be made to fit if you really want it to.

Cheers
Jon