the local tire shop says i'll need adapters,is that safe at high speed?

Is this a shop that has a lot of knowledge in rims, if not, you might want to locate a shop that has a lot of knowledge in regards to aftermarket rims, and they should be able to tell you the saftey factor.

yes, how fast do you want to go?? ie. my fathers friend HAS to use wheel spacers on his pro-mod for the calipers not to hit. 11.80s @ 92mph---yes, he let off the throttle