I would buy a new old stock boot. 50 year-old rubber is still way better than today’s junk. Also I just had a trunion converted to a slip joint for the A-100 truck and it has gotten very expensive in parts. Parts are over $400 the shop only charged $100 to do the conversion and balance it. They hadn’t done one of these conversions for a little while and were totally shocked at the price the parts were. They said the last one they did the entire job was less than the parts they bought last month for me.