Hey Gordon,
I've decided after all NOT to use the Crosman spring. It was bent, slightly rusty, and the ends were very poorly finished. Luckily I was able to source out a "premium" after-market spring for about $25USD. The difference in quality was amazing! The aftermarket spring was beautifully polished, coated, and completely straight. However, the wire thickness is 0.130", 10 thou thicker than the factory Gamo or the el-cheapo Crosman which undoubtedly came from China.
This required a new bushing (rear hat) that was 0.350" shorter. It took 10 minutes to spin a new one up and it works just fine.
The rifle now is a little harder to cock because of the new, more powerful spring. The recoil characteristics are slightly different too - it took about 40 rounds to relearn my grip and get 3/8" groups again. Honda Moly60 was used and a length of shrink tube was installed on the top hat where it contacts the mainspring. The rifle is quieter, smoother, and virtually all "twang" is gone.
I don't have a chrony yet but I have noticed that Gamo's PBA pellets now exit with a LOUD and distinctive sonic crack, much louder than with the factory Gamo mainspring.
All in all, I have a nice shooter again!
