anyone familiar with Gemini exhausts?

Just recieved my first Kz1000A1 after selling my MkII in 1989 and it is wearing an unfamiliar 4-1 exhaust by Gemini of Corona, Calif. the collector is huge with a 2.5" OD and ends with a round short Yosh type can that is louvered inside . I'm familiar with most of the aftermarket stuff for these bikes but have never seen this, if any of you guys who older than me (36) remember these from back in the day give me any info you have. thanks

if I remember right its a mac with an aluminum can.

There was one installed on the 1982 GPz 750R1 that I bought in 1987 and sold in 1989, but I’ve never seen a complete one since. There was a batch of NOS Gemini aluminum canisters for sale by a vendor at the Mid-Ohio VMD in 2024 that were exactly the same as what mine had. My recollection is that mine was made at about the same level of quality as the V&H exhausts of that period in terms of wall thickness and welds (painted black, not chromed). Not quite as good as the pre-Supertrapp era Kerkers, but surely less expensive and a good option since V&H didn’t make a canister-style for the 650/750 as far as I can tell. Better made than a MAC or Jardine, but it did sorta look like a MAC from a distance. Mine didn’t require removal of the center stand.  If I had one I’d keep in installed since it’s period-correct.  Hope that helps in some way. 

I know this is late and it may not provide what you are seeking. But there is an old post/topic here that used to have many pics of the different systems, at some point many of the pics were removed. If you want to go down the rabbit hole I have found it an interesting read. There is still good info there as many were posting size length ect. There is a mention on the Gemini as follows.
Gemini 4-1 (at least, the can says Gemini on it)
Primarys 1.5" OD 28" long
Collector 2.5" OD 10" long
23" from the end of collector to end of can
2.5" piping, 3.5" can

Anyway, here is a link the post/topic
kzrider.com/forum/2-engine/271747-header-pics?start=0