My best estimate is there are 25-30 running "GT40s" in California. My definition of a complete car is , it has a license plate on it or is currently running on track as a completed track car. I Know of about 14 people I can name, many who are on this forum. I would guess there are 1 or 2 real GT40's in Calif that I include in my total. The rest are several GTD's and quite a few CAV's along with at least 2 or 3 ERA's. Most of the other marks are represented here also, Tornado's, RCR's, DRB's, and homebuilts among others. I do not know of a RF here in Calif. but I wouldn't be surprised if there are at least 1 or 2.
There are about another 10-12 cars elsewhere west of the Rockies. Another group in the middle west, a few more in The Republic of Texas and in the south and about as many on the east coast as on the west coast. Maybe more as ERA's came from the northeast and have been around for quite a while along with most of the real cars in the US.
Sorry I don't count Kelmark GTs, Avengers, etc. It's just me so don't get offended.
All together my guess is about a 100-125 running (compete) GT40's in the USA.
I would be surprised to find that England had any less than the US and for the rest of Europe I am wildly guessing the number at about 1/4-1/2 that of the UK. Put that at another 25-50.
Asia... I include Australia and New Zealand.... would be about the same as Europe????
I would also guess there is something approaching the same number as completed in progress or laying uncompleted (dormant) in someones garage somewhere here in the USA. I wonder if this ratio would bear out worldwide? About 1/2 of the total "kits" have been completed.
All totaled, I have come up with about 300-350.
For what its worth.