Originally Posted by chevyluv72
They no longer sell the 4L80 to C4 adapter new owner
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.