Ed,

i was pretty much set on the kit spinner until i started really checking things out, especially since it looks so scale for this bird.
none of the 3 backplates i have will sit square (flat to the drive washer)......all are touching the DW face on one side, but you see light on the opposing side, thus inducing a wobble, which since these cones already have an out of round consistency, induce even more of a wobble...............this of course is on the FT 1.60 twin which has a bigger DW than a 1.20 (not sure about the Saito's). so it may be fine on the smaller driveplated engines.
but like you said, at the below 9K rpm's we are running, it isn't that critical, or is it?.................my bugga-boo with these is that i'm an old Free Flighter who use to run engines in the 23-26,000 rpm range during competition, and any amount of out of round or wobble in a spinner could eventually destroy a prop or the whole plane, so it's hard for me to say, "what the heck here".......................
it's too bad that TruTurn doesn't make a 2.5", but since it would cost $40-50 bucks, it probably wouldn't compete too well with the $14.00 GP spinner eh?

anyways, i'll learn to live with it, and use the GP spinners for static display.
i'm also forwarding this topic to Romco.........you never know