Hard to say, and I've no direct experience.  I'd call the subframe manufacturer and ask. 

In my experience there's no such thing as a bolt on exhaust kit for these cars.  I just put a Magnaflow kit on mine.  Really happy with it, but I had to fab pipes from the headers to the X-pipe, I had to chop 1.5" off the muffler end of the X-pipe to get the mufflers to sit right, and I had to fabricate half a mount for the tailpipes on either side in addition to welding their mounts onto the pipes.  Again, not complaining, but I've been spoiled working on newer cars where an exhaust just replaces the stock system and looks/sounds better while increasing performance.  Keep in mind that these cars had a single transverse muffler from the factory, not dual mufflers, so the mounts for that kind of system don't exist on the car and there's work to do to make it work. 

IF you can can snake the exhaust tubing over the connector.  Typically the pipes do run on either side of the driveshaft, tucked up into the tunnel a little.  BUT, my concern would be trying to get an H-pipe up into that space with the connector in place.

Looking at that system it looks bolt in.  Gotta be honest, not a fan of bolt in subframe connectors.  They do work, but you're placing all the stress of the connections into two bolts going through a subframe that's not designed to be loaded like that.  In cars that really need them I've seen those bolt holes elongate and even tear.  There's also the concern about crushing the frame rail when tightening the bolts, unless they use sleeves to prevent that.  I don't think you'd want that system welded in either due to how much it restricts access to the driveshaft, exhaust, parking brake cables, etc.  The brace across the rails looks beefy and trick, but from an engineering standpoint is only going to provide minimal torsional rigidity.  Its still in flat plane with the rails.  You'd be better off welding in simple rail connectors that turn the front and rear frame stubs into a cohesive member.  Such rails won't twist, and if you have enough power to twist them; a flat brace across them isn't going to help and its time for a rollbar.  The issue with the bolts in torsional rigidity is that you've created moment connections at each bolt, where shear forces will put stress on that connection.  Its not initially trying to flex the subframe connectors, instead its trying to shear the bolts, failing, and then jamming the bolts into the stock frame stubs, BEFORE applying any force to the subframe connector.  When the connectors are welded in the forces act directly on what has become a solid, one piece rail, and there are no moment connections. 

TKOPerformance wrote:

 ...system it looks bolt in. 

The subframe connector are weld in.  The tubing cross members bolt onto the welded subframe connectors.  It's actually 3 separate parts that go together.    The cross members can be removed if necessary.  

Okay, all of that makes a lot more sense.  In that case I suppose all you can do is try it, but if it worked for Al that's encouraging first hand experience, and it'll probably be okay. 

Whenever doing any chassis work the vehicle should be supported with the weight on the wheels.  You could in theory support it on the axlehousing in the rear and lower control arms in the front.  That's no my preference though.  I built a set of 4' tall platforms I can set a car on using my lift.  This allows me to roll around under it and comfortably work while the vehicle's weight is supported on its wheels.