CG from what I recall is right at the wing-spar. I've got one about 12yrs old(my oldest survivor). I installed an ASP .91 a few years back, and take it out flying about once a month or so, and it's an extreme machine. If you have anything around in that size engine, I'd recomend upping it, it's makes for one hot-doggin plane..
With the .61, I'd concur that a 13x4 might be a good place to start. I run a 14x6 with the .91, and it pulls out of hovers decently with that, while still maintaining sembalance of stability.
If you've flown the plane alot in years past, just start with minimal throws for first few flights, and after a few flights you'll want more. The older planes are like an old favorite pair of shoes to me, put them on(fly them), and after a few minutes its like you wore them yesterday.
I love my SHots. It's one of the funnest, even after all these years. Have fun, and good luck.