Thought I'd have some fun and draw up a manifold in solidworks. This is what I came up with. Using steam pipe from the prochem catalog. 50mm pipe. Designed with almost no cutting of metal until the merge collector. 
Turbo is placed around 50mm lower than original as I'm guessing this would be the drop that the T3 adaptors have, can anyone give me this dimension?
And I've moved the turbo around 20mm more to the centre. Hopefully this wont hurt anything.
Waste gate position isn't exact, I will make it more 90 degrees to the outside runners, at the moment it is 90 to the inside runners.
I am going to install a T3 turbo pretty soon, and I understand that the adapter is all I need but I cant find one for less than $90. So I thought i'll draw this and get a price on all the bends. I'll probably still go with the adapter in the end but this could be fun to make.
Any thoughts or improvements I could add?



 

looks like a full race jobby.
 
if you can dimension it then it should be easy enough to build.... dimensioning looks tough lol

Everything is dimensioned and pretty much all fully defined, all except where the pipe meets the t3 flange since the pipe doesn't mate perfectly flush with it, I defined the flange from the 3S flange at 15 degrees.
Just looking at the full race one now. It's turbo is a lot more central and high. The runners are quite different though, mine symmetrical where full race doesn't move forward of the number 1 exhaust port. I better check if there is a reason for this, maybe mine will be to close to the oil filter. I like the more central turbo position as it would be easier to make.
Here is the full race
http://www.full-race.com/store/turbo-manifolds/toyota-celica-mr2-3sgte-t3-prostreet-turbo-manifold.html
 

the full race also has even length runners..... just a thought.
 
yours seems to have two short and two long so you'll get a pulsed effect on the turbine that will change frequency as the revs (and gas velocity) go up.

Is it that detrimental not to have equal length? could it result in turbo failure? The standard one seems to do fine with a large variation in lengths.
By the looks of the full race picture it is not equal length. I'm finding it hard to draw up a ram horn design with equal length.

equal is good cause it means even pulses across the rev range.... it's more important for NA cars rather than turbos... it's possible to tune the lengths to get even pulsing at a certain rev range bla bla bla...
 
for a turbo having unequal lengths could result in pressure waves from 2,3, or 4 cylinders arriving at the turbine at the same time causing a sudden load on the turbo and its bearings... so you can open up fatigue issues and vibration issues or you might get weird harmonic issues....  from memory you CAN use these pulses to your benefit by capitalising somehow on increased kinetic energy potential but it's pretty high end stuff generally used for WRC or Indy and the like... (or F1 when they ran turbos).
 
 
all that said, you're right, the majority of manifolds aren't tuned length or equal length and they seem to work just fine. I guess it's just something that might be built in when you pay big bucks for that genuine TTE WRC manifold... its not JUST a nameplate.

Dont worry about unequal length, is the standard manifold equal length?  No.  Pulsing isn't going to make your turbo explode.  Dependant on the cam you are running it could hurt with reversion effects though, if the cam is mild this will be less of a problem.  Oil filter is always tight on the manifold, you may well run into problems, perhaps relocate it?  Dependant on the turbo, also watch for fouling on the transmission/clutch slave with turbo attached to manifold.  I have header flanges available in 1/2" steel.  I cant remember what they were worth, $40-45 rings a bell.

Turbo is a GT3076R, oil filer is already relocated so that will help.
I can get flanges laser cut through work easy enough, thanks though.
If I do decide to make this, is steam pipe a good idea? it would weigh a lot, or would properly braced tube be better?

How are you welding it, GMAW or GTAW?  And who/how much welding experience do they have?  I've found steam pipe manifolds in general to be very robust.  Especially using the GMAW method and not linishing the welds back, obviously experienced GTAW would also be just as good.  I'd not really recommend tube unless your welder has alot of experience, it will likely crack, especially if you are building a budget manifold with cheap materials.  
 
Steam pipe is reasonably heavy however nothing compared to the turbo.  Also, I'd recommend 1 5/8 or 1 3/4" pipework maximum.  2" is far too large for that turbo, you'll find it very unresponsive.  I've used a 1 5/8" steampipe manifold with a GT35R and produced over 500whp on 98RON.  2" is GT42R territory. 

I would be getting a professional welder from work to do it. Very confident with their work. 
Thanks for your insight on the pipe sizes. I first went with 2 inch as the inside area is the same as the manifold gasket on the gen 2, the gen 3 exhaust ports are even bigger so wouldn't it be detrimental on a gen3 going smaller than 2 inch? This is for a gen2 so if you think smaller is better I'll do that. 
Prochem dont list the sizes you recommend, only 1.5 and 2 inch. Do you have recommendations on where to source pipe? is 1.5 inch to small? this is smaller than the exhaust ports. Thanks for your input