Unfortunately with both of the cars you are looking at - you will have issues with negotiating the price. As stated in both ads, both cars are listed at cost price to the dealer. Theyre just looking to break even on them, rather than suffer a loss. No profit will be made by them on either of these vehicles. You would have a problem talking ANY dealer down past cost price, not just Dennis.
Usually in terms of test driving their cars, due to expense, insurance and all of the cars being unregistered, Dennis usually takes the trader plates and takes you for a ride in the car. I'm not certain if this is the same for the NAs, this is simply how it went down on my GT-R - and for an asking price of 25000 its completely plausible to do so. JapCars are generally happy to see you whenever youre available, will take you for a test drive when you want to, etc. Theyre very friendly, honest and laidback where their cars are involved. Their mechanic Bob once told me, when i was looking "whats the point of selling a lemon car? You spend a lot of time and money trying to make it right to be sold and then if it still has problems it just keeps coming back and costing you even more time and money" - so generally speaking all the cars there are pretty much faultless. You should be fine.
Let me know how you go - and once again, make sure you tell the guys i said hi =b