I wrote the following a few days ago so it may read as if I have not read a few posts. I saved a draft, intending to tweak it a bit before posting so it would read better but I don't feel like spending more time on it so posting as is.
From what I've read, the MM 7.5 HP Lifan 212 has a unique exhaust port so a typical clone header flange would not match the port and thus not flow well. If the round port is as large as some say (I have not seen a measurement but the port has been described as "huge") the engine may benefit from slightly larger tubing than the typical 1" OD to match the port (depending on how "huge" that port actually is, or isn't). I read, somewhere(?), that the MM 212 has the highest flowing head of all stock 196/212 clones.
The Pro Series is not a typical minibike so someone who does not have a Pro Series on hand will not be able to fabricate a header that will fit well, IMO. Without the bike, someone might make a header that won't clear the frame, fender, etc, or it may hang way out in the breeze. The only way to get what you want is to fabricate it yourself, or provide your bike, provide explicit instructions and pay someone else to do it. You could cut/fit the pieces and have someone tack them together, test fit the header, then have it welded when you are satisfied with it.
I'm not sure how you intend to use the iron plumbing fitting but the use of plumbing for exhaust is a pet peeve of mine so I would never recommend doing so. But, it's your bike so do as you wish. My advice would be to fabricate a header that will accept a low/no restriction muffler or just keep the stock exhaust. The stock exhaust is probably less restrictive than a header with a hotdog muffler. Basically, there are two things that quieten exhaust, volume (space) and restriction; a hotdog muffler has very little volume so it has to rely on restriction. That's why modern sportbikes have large mufflers (most now have a hidden muffler under the engine in addition to the visible one(s)), to use muffler volume rather than restriction to meet sound level regulations. On a minibike, there just isn't room for a large muffler; well, I guess you
could strap a car muffler on somewhere if you wanted to bad enough, but you pretty much have to choose quiet and restrictive or loud and low restriction. There are only two types of mufflers that I like for a minibike, a 28mm inlet aluminum pit bike muffler ($15 and up) for a modern look and the Lossa Engineering stainless steel reverse cone muffler ($100) for a vintage look. Both are straight-through mufflers so they won't be quiet, they will just tone it down a bit. If I wanted quiet, I'd probably just keep the stock exhaust.
If you ask for advice, you will receive some that you don't like. Do your own thing. Just warn me before you post any pics or video of a plumbing exhaust so I can hit the "Ignore" button.