I checked with a few friends, and I got one response as follows:
"I could only find one reference to the Hendrickson in Neme's Soft-Hackled fly imitations, but it was Ted Ward's Nymph and Emerger pattern from the Beaverkill.
* Hook: Mustad 94833
* Thread: Uni Dun 8/0
* Hackle: Grey Partridge
* Tail: 3 to 4 lemon wood duck barbs
* Body: Mixture of 2/3rds Sealex #110 and 1/3rd Sealex #117"
Now, I'm not sure this is the pattern you are looking for. Perhaps Syl has not yet publicized the recipe.
I will say that I've had some success fishing a Snipe & Pheasant during the Hendrickson hatch. Here's the recipe I use:
Snipe and Pheasant
Hook: Standard wet fly 12-18
Thread: Orange or brown
Hackle: Snipe or blue dun starling
Ribbing: Fine copper wire
Body: Three reddish brown fibers from a cock pheasant tail. For smaller flies, reduce the number of fibers
Snipe and Pheasant
Hope this helps some.
Mark