so, remove precat (thermal reactor) out from my 1986 NA (euro spec). going install full exhaust system. then found, that onto engine block, without 2 exhaust ports (below) are additional 2 smal (1/2'?) holes. what for?

block them with the flange or what? (quite well seen on http://www.rotaryengineillustrated.com/)

If your installing an downpipe, then you should not have to block or cover anything...?

No, actually I'm installing double pipe system from exhaust ports to the end of.

That why I took out precat (here we are calling thermal reactor)

A thermal reactor injects air into the exhaust port to help continue the fuel burning process. You can run a header w/o blocking them, however if there are holes coming out on the face that the header bolts to, they need to be blocked. Racing Beat headers cover those holes. They also used to sell blocking plugs for the air feeds into the ports for the old thermal reactor rotaries (pre '81) sold in the US. I don't know if the plugs would fit yours...