A lot of Brad Delp's really high register was courtesy of recording tricks performed by MIT grad and genius Tom Scholz h2o.

That's not to say he wasn't a really good singer though. When recording the first Boston Album... Scholz would use highly effected guitar notes to harmonize above Delp and create some of those mega notes... like the ones in "Long Time" and "More than a Feeling".

I saw both Boston and Kansas live back in the mid-late 70's and Delp NEVER could hit those notes. Steve Walsh on the other hand could and did.