That 305 will have plenty of power, especially with the 2-Speed Rear that you have. I'm guessing you only have a 4-Speed trans but along with the 2-Speed you will have 8 gears to use.
Also if you want more power and if it only has single exhaust now, add duals. Make sure you use straight-thru mufflers as these V-6 engines like to breathe. The straight-thru mufflers were also factory original.
Keep us posted.
Bill
