I am going to build an Ultra Stick 40 to use as a refresher trainer after many years of no flying.
I am going to build it as an electric and don't plane on fancy acrobatics with this one, at least in the beginning.
Are the JR 537 standard servos adequate for my building needs?</p>

Yup

TNX. I thought they would do just fine.

Yeah they ok but still expensive. I have Towerpro S5010 servo's in my Tempo trainer and they work just fine. I paid around $8 per servo but Ithink you may be able to pick them up for $5 if you look around.
Excellent torque, and on 6V they seem to centre just fine. Switched the plane over to a 4.8V NiMH pack and the Tower Pro's still seem to be doing the job more than adequately.

If you want a brand name servo then the Futaba S3001, s3003 or S3004 servo's are also superb.

But the TowerPro's are hard to beat when it comes to value. You can buy 3 for the price of 1 JR537.

Tower Pro changed it's name to Hextronix

So the HX5010's are the newer version.

Yep, I too run the Hextronic 5010's in all my 40/60 sized birds. They cost me $4.50 each from china and one set of 5 have over 250 flights on them!!!! They work prefectly. Never had an issue on any of the 12 I have. Some of the more expensive servos have slightly better resolution, but for the money they'll work fine. There's 0 slop and they center perfectly every time. They run perfectly on 6.6V a123 power as well, and put out a pile of torque.

I run an assortment of Hitec standard servos in mine at 6volts. I had another one that had a bunch of Cirrus and Futaba clones in it and it flew just fine on 4.8 volts. I really love the Ultrastick. I enjoy my 40 so much I bought a mini so I can fly it in the park across the street.