I wouldn't be opposed to spending $100 or $150 on a part if I was confident that it would solve a problem. But I worry about buying flexible parts that are almost 40 years old. For my day job I have done a considerable amount of study on the durability and ageing of flexible membranes. I don't know what material was used for these diaphragms, but for many flexible membranes, the flexibility comes from the addition of plasticizers that will disappear over time. Like the difference between a flexible PVC pool liner and a rigid PVC pipe. The both use the same PVC monomer, but the pool liner is flexible - at least at the time of installation - because it has been compounded with plasticizing agents. For anyone who has taken out a used pool liner after 20 years, at that time they can be as brittle as potato chips as a result of time, pool chemicals, and sun causing the plasticizers to migrate out.
When we had our Interceptor it came to us with no accelerator pumps. I tried for a while to swap in LTD carb bowls but even then had trouble finding LTD carbs that didn't come with their own set of problems. After a conversation with Keihin US, they directed me to a "sister" carb that they made at the time that was supposed to be a direct swap. I think that information is in another thread here. I will also look in my files to see if I can find that information again.
Today, if I could have done it all over, I would swap in the Mikuni carbs. They may not be as sophisticated as the Keihin's, but they certainly are simpler to work with. And on a side note, the heating control system in my Honda Accord is manufactured by Keihin.