I have seen references to a Passport v3 cart allowing you to play US carts on a PAL system. However, in my experience .... I've had 2 similar cart adapters there are significant issues due to the fact Nintendo cottoned on to this pretty early and as a result released several different CIC protection chips to stop this occurring. They had seen this occur on the SNES so went into the N64 with their eye's wide open to this workaround. Oh ... and you need a NTSC capable TV although what TV isn't these days ....
As far as I can tell you will need an original PAL cart for each CIC chip to match one on the US cart you intend to run or you will see the dreaded "Not designed for this region" error. Even then you may find games that just wont run. I had both US & PAL Hydro Thunders and it still didn't work with my adapters.
Seriously ..... just buy an old US N64 off EBAY for a few bucks. You can use your existing PAL power adapter on it along with all other accessories and it beats mucking around with carts....
