[Mayvik]

As far as prices for a mod (if needed) you'd have to check on the airsmiths forum, ask Rainman. I suspect it won't be a lot, just a pass or two with a ball nose mill if the diameters are different. Otherwise it may be a screw hole issue which might be a simple drill and tap or two. It's hard to tell what fits what on STBBs, because the frame attach tends to be one of the most common "proprietary" changes between brands.

Have you actually tried fitting a standard Spyder frame on there? I know the Millennium is a "fatty" striker body but I'm not sure if that changes the frame mounting at all. Also, if I recall correctly you can fit Intimidator frames on there, so if you have access to one of those you might try that as well.

PS: Might want to ask this on the Kingman forum on PBN. Probably 1/2 your responses will be retarded but there are a few great Spyder modders over there as well.