The Allison 501-D13 FAA type certificate contains a formula to calculate the equivalent shaft horsepower provided by the jet thrust as barit1 and Erebus alluded to in their posts.
Equivalent shaft hp = (jet thrust lb)/2.5 + shaft hp
The take off (5 min) rating is 3750 ESHP, 3460 SHP and 726 lb jet thrust
Max continuous 3420 ESHP, 3138 SHP and 705 lb jet thrust
Formula given by Kieth. Williams. is what I learnt near 50 years ago also.