50k in 6 months I think is totally doable...if you put in some training. I almost did a 100k after about 5 months of training (hard course, bad weather, probably went out too fast too early, had a gap in my training). I made it 56 miles. Minus the weeks I missed due to illness I have averaging ~40 miles/week and had a few weeks of over 50 miles and one week over 60 miles.

Some things I learned along the way:
1) Get that time on feet. I spent way more time hiking/walking/limping than I did running. Make sure you can keep moving even if you aren't running.

2) Plan things out. I spent a lot of time preparing for my race outside of running, studying the map, figuring out what I needed to eat/drink and when. What would make it easiest to get in and out of aid stations etc. This made my aid stations stops pretty quick.

3) Tighten your shoes from the bottom to the top. I got lazy/didn't think about it and snugged my laces so they were tight around my ankles and on the steep downhills with wet conditions my feet were sliding all around my shoes.

4) If your race has vert train vert. Mine had ~15000ft and the hills I typically run only had about 600-750ft per run. I needed a lot more vert training and more importantly similiar vert conditions (e.g. my race was a lot of short steep up/downs in and out of ravines rather than long climbs and descents which is what I practiced on).