Xe268 cammed 360 and very light body

The best bang for the buck is a higher stall converter and rear gears. Couple these items with some good sticky rubber and a suspension that works well.

For the engine itself, stop where you are and ether stick with the plan or create a new one before any more money is spent. Otherwise it’ll get really expensive.

IMO, there is nothing cheap about a turbo even from eBay.

What other components do you have for the engine now?
Intake? Headers?
What is your current gear ratio?