It's your choice of coarse, Steve, but the cost per HP gained when tuning the CVH is simply not worth it, there are better engines around! 1.8CVH as std = 90bhp Vs 135bhp for a std 2.0 Zetec. you can get a decent Zetec for £150 and you won't be able to do a stock rebuild on the CVH for that.
Like I said I wouldn't waste the price of a gallon of engine oil on it. Just use it to get the car built and on the road if you don't want to mess about with engines at this time.
Note also should you ever choose to sell the car at a later date it'll be worth more with a zetec than the CVH
