2006 – 4L80E in C4 Corvette Adapter Kit (1984 – 1996). Swap your 700R4 / 4L60E transmission to the much stronger 4L80E transmission with our new double strength case hardened output shaft and adapter kit. At this time we have in development an adapter kit for the C4 Corvette to replace your 700R4 / 4L60E transmission with the much stronger 4L80E transmission. This 4L80E transmission will be the same length as your 700R4 / 4L60E transmission making it possible to reuse your existing 27 spline driveshaft and C-beam. This is the worlds first 700R4 / 4L60E to 4L80E swap direct replacement. All that needs to be changed on the 4L80E transmission is the tail housing and output shaft. The full manual shift model works without a computer. We are also working on a C4 Corvette 4l80e
I think those C4 4L80E C beam adapters were made to order by PATC Monster transmissions.
They never were real popular and it was expensive at $650-700 I recall.
Just a small number were made and sold.
Maybe someone bought a spare kit.
Best way is network on Facebook C4 Groups.
No Racers on those groups.
Mostly cruisers and kids.
It was a 1 off billet aluminum Tailshaft housing.
And a Turbo 375 Output shaft.
TH 375 was made 1975-1979 only for Fullsize GM cars with a 400 SBC or 400 Pontiac V8.
Turbo400 with a TH350 27-spline output.
To duplicate at machine shop costs it would be over $5k.
May be possible to build a steel cage around stock 4L80 E output to mount C beam.
It may not be.
It has only been done that way 1 time with a TH 400.
If you use a conventional race car Fabbed Crossmember the Dana 36 or D44 will explode or Batwing cover will fail.
C-beam takes up torque reaction.
Other option is Solid axle it.... $5500 conversion kit.
I would go TH400 myself. But that is me.
If you use a 700R4 or 4L60E it may last a while.
Plan on rebuilds every few months.
Big Blocks have mega torque.