I aggree with all these replies
The Medusa motor, being a 4 pole motor will outpull your old motor by lots, and run cooler doing it.
If you want to match your old top speed, go with a 18 tooth pinion.
If you want a higher top speed, go with a 20 tooth pinion. I'm sure the Medusa would have no problem tossing it around with this gearing. As long as you're still close to the stock vehicle weight.
Nice setup btw.