Catalytic Converter, O2 Sensor & EGR Questions

[Von]

I have a 94 Suzuki Sidekick JLX 4x4 with a 1.6L 16v engine. The PO removed the catalytic converter for some reason and now is straight piped. I installed the Doug Thorley 4-2-1 header on the vehicle for it came with it when bought but was never installed. The header will not meet with the existing mid pipe and the flange is different. Before I cut and weld the proper flange to the mid pipe should I get a cat converter and install. I’ve heard the EGR needs the back pressure from the cat to function properly or it will throw a 51 code. Is this true for this model and if so should I put the cat back in? I have no emissions laws where I am from so this question is purely to make sure it is running properly.

Thank You

yes, cat back pressure makes the EGR work. (modulate)G16 engines
but code 51 is USA cars, is yours USA?  many cars in canada (all really) have there own ECU. (market code 28 ECU = canada)
if you open the hood and look up , and under and you see the USA smog sticker there from Suzukik
in the center it tells you USA EPA regulations or California. like this.

https://fixkick.com/specs/Body-TAGS/html/image_8.html

if you see that word USA< that is  Code 51 ECU.. by law..
the other down side, of no CAT is this..
1: hot summer day and engine.
2: parked at  RED light, for 10 min and windows down,  or worse 2door car top down.
3: the stench of raw exhaust,  can be really bad. drifting from rear to front of car..

that is it on EGR,  EGR can be very hard to get working , due to carbon build up in all paths.

So I will be getting a Cat converter then and will have to check out my EGR for I’m almost certain it is clogged by PO not running a cat. EGRs are more expensive than I thought on these vehicles. Any helpful cleaning tips would be appreciated here. Also is it ok to install my cat right behind the Doug Thorley header or do I need some space pipe between the header and the cat? 

Thank you