...thinking of installing a clifford 6 into 2 header on my I6.
...wondering if I can mate the header to a V8 exhaust, and use that V8 exhaust when I go to the V8 engine conversion down-the-road....
Any comments / advice appreciated.

Thanks.

 

You could do it but the pieces between the V8 exhaust and the header will need quite a few bends

 

+1 with DazeCars, you'll need a couple - not a lot though. You can use the stock exhaust out of a V8, just up front will change. Quite a few people have done it, but I can't find where I saved those links...

 

Just run a single exhaust for now.
Install duals after the V8 swap. Then everything will be fresh.