Thanks for the responses so far.
I called Hergesheimer today and when I asked if they could do a PPI on a 914, the person I spoke to said they rarely saw 914s, calling them "vintages". He then asked me to hold while he spoke to his mechanics about whether they could do it. He returned to the phone to tell me "Yes we can do it", but it didn't win my confidence, even if only for a PPI. He was kind enough to give me a referral for Aase located in Fullerton, but that's too far.
After calling over 5 shops and getting multiple referrals, I got a referral from Vision Motorsports for a fellow named Greg Armstrong at Historic Race Engineering in Costa Mesa. His shop apparently isn't much to look at (so I was told), but he apparently knows his stuff and is entrusted with incredibly rare and expensive cars. And he apparently knows 914s. I called him today and set up an appointment for Monday. I'll post another reply afterwards to give a little report.