Ok..don’t laugh as I’m new to this stuff.
Does a 1.8 exhaust fit on a 2.0 motor..I tend to think so.
Any sound advice is much appreciated as I’m about to embark on a 1.8 to a 2.0 complete transplant.

Thanks in advance.

If you have an SSI system then yes,the ID of the exchangers is the same as the 2.0 counterpart. I did once put a stock 1.7/1.8 system on a 2.0 in a pinch but don't recommend it as the Pipe ID's are smaller and would be a bit restrictive. I however did not notice a difference on my healthy stock 2.0 motor

Thanks for the response / advice

The heat exchangers,hangar on the trans, and muffler all have match.A 2.0 muffler wont bolt up to a 1.8 heat exchanger without modification and the trans hangar is diffrent from one exhaust to the other.As long as you have all 3 components it will swap from car to car ,engine to engine .

I just went thru this myself, and here is what i learned.
I have a 75 2.0 , needed new h.e. and exhaust. The stock 75 h.e.'s are very restrictive, and tended to warp and crack, also run hotter, more restrictive etc.
So best to back date to 74 or so.
I bought a set of H.E. on this sight, they are SSHE can be expensive but I got mine from a guy parting out a car, they were $300. but usually are 4-500.
Anyway there is a difference from the 2.O to the 1.8/1.7.
At the muffler end, the 2.0 are straight, whereas the 1.8 will curve up, so here is what matters: the muffler and the H.E. must match, and have the proper muffler hanger, but you can put a 1.8 on a 2.0 motor, they just bolt right up, you just have to make sure you get the right muffler.

I have 75 2.0 with 1.8 stainless steel H.E. , dual outlet muffler from Dave at Triad.
Big improvement- his mufflers are custom made, good sound etc.

i will try to attach a couple pictures.

Phil. P.M. me if you have any questions.