[KTL]

If you really want to be budget-conscious, you can bore and replate your 3.2L cylinders to accept the 98mm 3.4L pistons. Places like EBS Racing, US Chrome and Millenium Technologies.
Plus i'm sure somebody would like to have your Euro 10.3:1 pistons, which would offset some cost by selling them. The key is to make sure your replacement pistons are sized to your replated cylinders. So you need to obtain the new piston diameter in order to be able to specify the bore sizing/piston-cylinder clearance.

If you're doing higher compression pistons, you'd be foolish IMO not to select a more aggressive cam profile.

Valve job is not uncommon on the Carreras in terms of valve guide wear. If you have worn guides worn beyond allowable spec, the valves are probably in need of replacement. I needed all new valves on my '87 top end years ago. New valves are a little pricey on the exhaust side. Intervalves makes a good quality valve, so those can save you some signficant $ over OEM Por$che valves.

You'll need to get your chip remapped for the increased displacement & cams.