I like your solution!
When i was looking into this part of my build i was reading some of the lo-cost forums and how they had to do things for the IVA and i came across the 7/16 threaded, 1" long weld-in tube adaptors that a lot of them have used:
http://www.ebay.co.uk/itm/7-16-UNF-R...-/380129249524
I've used some of them on mine due to reusing the MR2 seatbelts i had laying around and i can heartily recommend them.