There was a person not to long ago that was casting some bullet grade metal heads (brass I think)
What are you going to use for the mould? And also it would be worth looking at pictures of 14/15th Century heads in museums as the socket is normally much smaller than what people make now. In fact most arrow heads being made at the minute now are much larger than what would be typical for the period. If it were me I would cut a few mm off the socket of the heads you have, which will also bring the weight down.
You have to also respect the time someone has put in to make those heads, you should at the least ask the original maker if you can cast them.
Valid points on each, the heads are made by Bearpaw products in Germany, so id get sued if they found out i wanted to do that LOL, so maybe not cast them, but about the socket length, yes a few MM of the back end would do it and they were made to fit mostly 1/2 inch shafts, the heads i have are medium sized they are half the size that the Saxons used, is love to get the Hector Cole Saxon type 1 arrow heads, they are larger and look alot better i finds, ive tried emailing them and got this email is permanently closed, and the phone number to their shop is disconnected