Right I have my plug made and ready to start making the moulds off it but after watching the video of the split mould using the uni mold kit, I bought one then realized that its no good for the new pre peg ' would it be possible to use the EL160 is a high performance epoxy laminating resin with the glass fibre out of the uni mould kit and use the EG160 high temperature tooling gelcoat ?
or if not would it be possible to make a split mould out of XPREG® XT135/S Tooling Prepreg .
Thanks

ps the problem with my car not boosting was broken spring in the turbo actuator ' a not very old high performance actuator at that but at least then sent me a replacement spring that i can fit myself 

That's brilliant Steve Hopefully the plug should be ready to take a mould from sometime next week ' as I've a boost problem with my car ' I'm going to smoke test it this morning to see if I've any boost leaks before I start checking the sensors.

I would make the join somewhere along the black line.

With the sides being quite short you would probably get away with parallel sides, as long as you use plenty of release agent. Just make sure nothing converges!

no mate High density polyurethane foam Block

This is the shape of my plug from the side 

Thanks again steve I'll keep your information in mind when i make my moulds 

No problem :-). The main trick is to make sure that you don't get a mechanical lock. There are a couple of ways to achieve this. The traditional one is to make sure that any parallel sides of the mould sections aren't exactly parallel, they actually move away fro each other very slightly. An alternative method that I have used is to make the mould sides (the sides that are bolted together)  slightly flexible when the mould parts are unbolted so it can be flexed, popping the part out. This method isn't usually recommended by experts or books, but it has worked for me :-) As long as the sides don't converge this works pretty well for certain parts. It worked on the above part but only just!

Having said that, i recommend that you go with the traditional method as I don't want to be blamed if you can't get the part out! :-) The taper can be minimal. If the sides are of a convex profile then there isn't a problem.