NGK of course with a BP5HS, B6HS leading the pack. I'd advise the BP5HS, it's probably the hottest plug you should use and best with the oil/fuel ratio recommended by manufacturers. There are platinum and iridium plugs, too. I'd leave them until you really get into modding the motor. A high compression motor pretty much needs one. Just keep an eye on the plug, check it for too rich and too lean conditions.
And as far as fuel/oil ratio goes many are recommending a 16:1 ratio, too rich. 24:1 is good for the first gallon or 4 liters then 32:1. There are some using a product called "Opti" or something like that and runs 100:1. I'm old(school) and that just isn't enough oil but there have been no reported failures from it...
There is another pipe. I have no experence with it. I call it the banana pipe. Problem with it is that there needs to be a length of straight pipe before the expansion chamber. It's used to tune the pipe. Changing this pipe effects the RPM the pipe really starts to work. Without it the pipe leaves a lot on the table as far as power production is concerned. Yeah, they make more power but not like they should. Some experimenting with a head pipe would lead to power gains I'm sure.