All the big blocks I have built for myself and others with KB hypers got .0025" piston to wall clearance set up as a fresh new build.

That said, you can run a little more, but it's not really recommended. If they are a domed piston and are in any way close to the chambers in the head, you may want to look at those clearances as the piston is going to move alot more. Also don't expect the the same ring and skirt wear as a tighter running piston.

On the cheap, it could work, but it won't be ideal for sure. But you already know that going in. And truth be known, would run ok for a cheap build. There certianly have been worse things done by others.