If you want to sell your Z I would use an online auction such as carandclassic, see the advert Evo above.
Take lots of high quality nice photos, undersides, close-ups etc
You get to set a reserve so you know you are going to be reasonably happy if bid to that price.
If it doesn't sell, follow it up with a traditional advert that you can run for a month or so until it sells, drop the price if no initial interest etc
Live auctions are too much of a risk with too many variables out of your control as seen at the NEC with the HLS30 subject of this thread. The auctioneer started the bidding on that car at £5k? Why? No other cars going through that I watched had a starting bid so low compared to the true value/where ended up. Should have been £15k at least, even off the wall to start the bidding off.
That car was worth £50k all day long yet the seller will have got less than £30k in his pocket!
The buyer in Switzerland got an absolute bargain.
There are international online auctions that cover Europe - collectingcars.com is one I know of and that car would probably have done much better on there. BAT in the States (not sure if their European venture ever took off) is another option but hindsight and all that....
I don't think I've ever seen a US origin lhd Z fetch decent money at a traditional classic car auction in the UK. Pre-online auction days, many years ago I sold a couple of HLS30's at different auctions (one also a super nice original early 1970 model at the first ever Silverstone NEC auction) and although both sold, they struggled to reach the low reserve set and left me wishing I hadn't bothered.
Rhd UK cars tend to fetch better money at traditional UK auctions so not a definite no-no if you choose the auction carefully but why take the risk and hassle involved when better and cheaper alternatives now available.