The Gearbox:
The standard MGB overdrive gearbox is not strong enough to take the V8, so a Rover 5 speed LT77 box will be fitted, it is ideally matched to the Rover 3500 engine.

 This is the Rover LT77 gearbox, complete with V8 bell housing. I also obtained a new V8 Vittesse clutch kit, new SD1 slave cylinder, and release bearing.

 The MGB gearbox cross member will need to be modified to take the new gearbox.

 I didnt realise that the dust cap that covers the gear lever was missing, apparently the tag breaks off and they get lost, and of course you cant buy them anymore!..

So... I made one. I found a gear lever cap with about the same dimensions, it was made for a Ferguson tractor, once I cut the top off, made slots in it and welded a bracket on, it looks just the job.

 The SD1 Gear lever will need to be modified as it sits slightly off set in the transmission tunnel.

 Following the engine and gearbox trial fitting, I measured the gearlever offset and modified the lever.
I cut the shaft off low down and removed the rubber damper inset, then weld on a spacer to set the lever forward and slightly to one side.

 The trail fit also highlighted the fact that I still had an auto gearbox dust plate fitted, with no provision for the slave cylinder, so rather than but a new one I modified it, by welding on an extra piece of metal and shaping it to suit.

I decided to fit a new clutch master cylinder, as the standard mgb one would give me a heavy pedal. The original all metal V8 master cylinders are no longer available, so you have to buy one with a plastic reservoir (GMC 1011), which hits the bulkhead when fitted and has to be modified. 
Here is how you modify a MGB V8 Clutch Master Cylinder to get it to fit. 

 Before modification

 Drill out the rivets holding the reservoir on, turn it through 180 degrees, trim off the plastic ridge and refit it using nuts and bolts. There was no room on mine afterwards for the top nut and bolt, so I tapped a thread in the mounting plate of the cylinder to take a bolt, which I then cut to the exact length.

It should look like this afterwards.


The early LT77 SD1 Gearbox has a poor reverse gear selector mechanism in my opinion, it has a strange method of a spring loaded plate which has to ping down when you select reverse, on mine this action was harsh and difficult to push the gear lever across the gate, so I had to come up with a way of improving it. No amount of adjustment of the baulk plate screws seems to help, so I obtained a few pairs of springs of the same diameter but with different strenghts and tested them. The original springs take about 7kg to start compressing them, in the end I used springs with about half that amount, this improved the selection greatly. 

Which gear oil?
The standard oil for these gearboxes is Auto Transmission fluid, however this has its limitations when using with synchromesh gears. 
A company called 'Difflock' do a specially formulated oil called Evolution 1, but is expensive, so I opted for Castrol Syntrans Multivehicle 75w90 synthetic oil (this replaces the old SMX-s oil), more reasonably priced and comes highly recommended.