I'd probably replace the other front tire, the Firestone, with a Sailun using the exact specs, size, and model designation.
Sailun commercial truck tires are of
excellent quality and have a very good reputation.
They are not one of my favorite brands and I personally would not buy them as a replacement were I changing out all my tires. But this is not because they are an inferior tire ...again, they are an excellent tire.
However, if in your shoes, I probably would go ahead and use Sailun tires on the steer axle because of the situation that is presented. I like having tires of like size, brand, tread mileage, and age on the front axle myself but it isn't imperative that you do so.
Now the reason I personally would not use Sailun as a choice to replace all my tires is strictly a personal one and has nothing to do with the quality of a Sailun tire.
Many on this forum, one in particular (LOL), will disagree with my stance but I still contended that Sailun is a CHINESE company and what I mean when saying "Chinese company," I'm referring to the corporate headquarters. The Sailun corporate headquarters is physically located in China (PRC !!!).
Now like all big tire companies, Sailun has many subsidiaries. Their commercial truck tires sold in the U.S., I believe are now all made in a factory owned by one of their wholly-owned subsidiaries in Vietnam. The facility in Vietnam is a semi-autonomous company but is still ultimately controlled by the corporate headquarters in China (PRC !!!) where some percentage of the profits made go to bolster the parent company in China (PRC !!!) ...again, the company that owns the Vietnam plant is a wholly-owned subsidiary (definition of "wholly owned" go
HERE or
HERE) of Sailun, I believe it's known as Sailun Vietnam Co., Ltd..
Sailun also has a wholly owned subsidiary in the U.S. or actually, I believe it's North America called Sailun Tire America which serves as their marketing arm here in the U.S. and Canada.
So for personal "political" reasons, I prefer not to consciously buy products where a portion of the profits end up in China. Yes, we all buy plenty of products made in China ...that is unavoidable. It's just that I personally do not want on purpose to buy a product where the corporate headquarters is in the PRC
if there are other alternatives. But I'd probably go ahead and do it if I found myself in your situation.
I tend to favor brands that come from wholly owned subsidiaries whose parent companies are in Japan, e.g. Toyo, Sumitomo, Yokohama, etc.
eta: keep in mind, what I just wrote is my personal OPINION. I'm not a tire expert. Many on this forum disagree with me on what I post about tires. So I just want you to know that I'm just bloviating and to take any advice I give as possibly not being accurate but just my opinion like a lot posts on this forum where people may have different views whether accurate or true ...or not. You ultimately must treat what we say here with a grain of salt and then do your own research and make your own decisions.