Can I swap a 78 dt175 engine onto a 76 dt175 frame? Wasn't for sure what changes were made to the dt175 engine throughout the years. 

I've never tried it, but I'm somewhat confident the answer is "yes, but....". 

Exhaust is different, intake boots might not line up with air box, shifter location and kickstart could possibly interfere. 

And then again, everything might work fine.  It's something you'll have to try.

There definitely was a major redesign between 1976 and 1978 but the basic engine design is similar.

My thoughts as well but I didn't think about the kickstart and shifter location. I knew the frames were different but didn't know if they changed the engine design itself. I bought a non-running 76 and turns out piston and rod bearing are destroyed and who knows what else. Found a cheap 78 and was hoping for a quick swap and temporary fix.

Yes the engine is changed but I don't know that it wouldn't work.  Kick start and shifter "should" be fine.  Just stuff to look at.  I can't say for sure they would be fine.

Where are you and would you sell the 1976 175 ?

THe 1975 exhaust comes around the right and goes out the left of the bike.

The 1978 comes around the left of the bike and goes out the right of the bike.   May be some issues with exhaust connections and lineup.