Combining 6/8 and 3/4 beat?

Hi. Can someone help me? We want to do a special Que Sera Sera Version. In the first part we want to play in a relaxed bluesy 6/8 beat, but at the end we want a German Oktoberfest Sway-Waltz in 3/4. Woom-ta-ta. How shall i set the tempo or do the patterns? The waltz needs double tempo? 6/8 = 84 BPM - 3/4 168 BPM?

With some thinking, I solved it. Here is a basic file - if someone is interested.

I’ve done the same thing to achieve half-speeds, but only using 4/4 timing. Very cool what you’ve done there.