There really isn't much to collector design on a turbo manifold. Choke diameter has nothing to do with it since all you are concerned with is a nice transition (low angle) to the turbine entrance, whatever shape that may be. There is no need to try and have some scavenging collector when the exhaust pulses are going to hit a wall (turbine) right after it. Don't put too much thought into it, equal length is not all that important either, being close does not hurt though for sure.

With a turbo that is only going to make 250-300whp the turbine is going to be such a restriction that designing a real good exhaust manifold is not really that important. This can be seen on alot of the old mitsu turbos that were so restrictive on the turbine side that tubular well designed manifolds really didn't make much power over the stock cast pieces.