Have no fear and take a risk. I had an old bench seat that was pretty shagged after years in the weather numerous pot plants decorating it. It resembled my neighbours but two slats had rotted through and a handle was falling off. Some slats in the back had rotted out. It’s was destined for the bin but I needed something to do so broke it down and replicated the rotten bits using opposite end pieces etc which I cut out of short sticks of pine I picked up from Bunnings. Some screws to replace the original dowels and glue. It firmed up good but the mix of timbers Kwila / merbau and pine didn’t Look great.
if you get this far forget the stains. PAINT.
Tools my trusty ozito 18volt drill and circular saw stainless screws and sellers exterior pva.
A good undercoat with British Paints water based 4in1primer sealer undercoat and then the magic happened bright orange Dulux water based enamel from the paint crew at Bunnings semi gloss gave a hive surface and the satin finish hid the imperfections from my wood work.
Sorry I missed this when you posted but well done.
I did a similar thing with my bench seat which had the traditional steel ends. I purchased new like for like timbers but in a treated pine and it has lasted allot longer than the original untreated pine but just a few weeks ago one of my boards broke, the one behind the knees which is strange, the one under the least pressure anyway, i'll have to take it off and replace it but overall the rest of it is still ok. I chose not to paint as it was an extra expense but your bench has turned out perfect and a good solution to paint it to hide mismatched types of timber and a really nice bright colour.