Has the bottom end been re-built already with the pistons and rods???

You need to have the block machined for 10 long studs and think theres a water pump mod you need to have done, you may as well get the under piston oil jets machined in at the same time, I would...

You need to contact a few engine builders for prices, I know Reyland do it, also Hart, x-power engines and field motorsport to name a few, I'm sure all or most cosworth specialists can get the work done