I believe the MBM MC309 will work for you.
https://mbmbrakes.com/mc309-gm-1967-...ster-cylinder/
MBM description:
GM 1967-1977 Cast Iron with Bleeders
1-1/8" Bore; Deep Hole
9/16" & 1/2" Ports on Left Side with Bleeder Valves
Licensed GM Restoration Part
Exact Copy of Original w/ casting number 5468309
There are a few on line vendors.
Be aware that there
will not be a residual valve for the rear drums in this MC. They do recommend the use of an inline residual valve but it is not absolutely necessary and say to use one at your discretion.
I am not sure of the 69 models but according to the 68 service manual all models used a 1-1/8" MC with Disc Brakes
Also, Tuff Stuff Performance has a selection of MCs 1" or 1-1/8" bores with deep or shallow piston holes.
https://www.tuffstuffperformance.com...cylinders.html
Dave