1. Will my 2005 D3 ARB Bull Bar fit. No
2. Will my Kaymar twin wheel carrier fit. I think it will but double check with Kaymar
3. Will the Safari snorkel fit. I think it will fit but will be next to useless as the V8 breathes through both LHS and RHS vents.
4. Will GOE 18" wheels fit a D4 V8. Yes.
I sold my D3 with only one of the wheel carriers and kept one for the D4, this saved a bit of money. If I did it again I wouldn't get a Kaymar rear bar I would just get a rear carrier and keep the original bumper.
If you are thinking of getting an auxiliary tank be aware that the V8 is different to the diesels and the D3. The charcoal canister needs to be connected correctly or you will have problems.
Also be aware that the resonators at the rear of the V8 exhaust are very large and will likely hit the brackets for any auxiliary tank. I had mine removed and there was very little noise increase.
PM me if you have any specific questions regarding the V8, I've had mine for over 3 years now.

