AHHH, just re-read original post lol. Where did he get the starter, and was it a rebuilt, one or a new one.
I don't know what everyone else was thinking, but on the whirring sound here is the scoop.
If it makes a high pitched whirring sound 1 of 3 things is happening. Either the starter gear is moving out towards the flexplate and not hitting it thus needing shims. Which BTW, I haven't had to shim a starter in about 4 years, you don't use them on anything newer now a days. That was a like pre 90's thing except for like 302's and LT1's that continued in their design into the 90's.
OR
The starter gear is spinning, but not plunging out towards the flexplate. Thus, shitty starter, likely a poor re-build.
OR
The flywheel/flexplate is loose
If a tooth was missing it would make a clanging/grinding sound then typically catch, then have a dead spot of clanging.
In 1 RARE instance on a manual car, we saw that the outer ring of teeth on the flywheel broke off (LOL) causing a whirring noise due to the starter gear not being able to reach the teeth.