My guess is you want a string 2-3" longer to end up with a brace of 6.5-7".
Larry Nirk and Nirk Archery are somewhat of a mystery to some of us. I've seen various posts and comments elsewhere that inicate Randy Dehnel worked there, but that was refuted by Mr. Berry above...and I should think he would know. BTW, I have noticed the writing on the Nirk bows is about the same as found on Saxon.
The Nirk company seems to have been primarily an arrow, nock, and accessory company rather than a mfg. of bows. I just do not know if Larry Nirk was a bowyer, but heard he had about 20 or so employees working for him.
Maybe if you posted this on the collecting/history forum, some of those guys may be able to shed some light on Nirk. Also, maybe Mr. Berry can fill us in on what he knows of the company.
Good shooting to you...