I have to admit, 250gr. on a full length 1535 with a 50# bow, sound awful strange. I think I would probably check the draw weight of that longbow with a scale first, and then call the bowyer. Find out what he recommends.
It's important to know how your riser is cut in relation to the center of the bow when trying to match arrows to a bow. It would really help you if you had that information for your recurve also, to use for comparison against your longbow.
I know one time I was tuning some arrows and was all the way up to 300 gr., come to find out I had it backwards, it was to weak and I thought it was to stiff and went the wrong way. Ended up at 145 gr.
Hope this helps!