FI Down pipe, flange is gone

[DeltaV]

I have an '82 Spider to which I'm trying to fit a standard exhaust. It appears that some time in its past, a former owner had a catalytic converter just slip fit (and possibly welded...too much corrosion to tell) over the down pipe, and had the 4 bolt flange cut off. Then, the exhaust is just cut past the cat (which has no flanges on either upstream or downstream).

I'm trying to install the test pipe (w/ 4 bolt flanges), along with the standard resonator and muffler, but can't figure out how I'm going to install the test pipe to the down pipe. Are there any adapters that I could get? I haven't been able to find much in our size range (these are what, 1 3/4" pipes, right?).

Thanks