Cusser
+1y
New engine might have more resistance just by being new, and how long did all this take, battery may be low. Did you try a jump start?
Yes, the voltage should be 9.6 volts or higher while trying to crank. But still could be a bad starter pulling too much power, or maybe just getting hot because it's under such load.
Jump starting or putting in a known good batter (assuming terminals and cables are clean and good) is a lot easier than pulling the starter. But AutoZone and O'Reillys will test both for free.