Hi there - I think you posted this question on my website guestbook a couple of weeks ago?
We didn't have the Hedlite cap in the UK, but from what I can tell by comparing the non-Hedlite 700 and 750 caps, you'll find they're both the same diameter, but the 750's is 'taller' than the 700s. You might be able to get it to fit by using longer screws to secure the 750's cap in place, but as to wiring it into the circuit, I couldn't say for sure.