O.k..... Lets look at it this way.
How fast do you want to go?

A CA18DET with a T28 turbo out of an SR20 & a chipped std ECU, a LSD & some sticky tyres should see you well into 12 sec. 1/4 mile territory.
Anything beyond that & you're looking at cracking open the motor to add forged bits, cam etc.

You can get the same sort of results out of an N/A SR20, but because there's no turbo, you're looking at cracking open the motor straight away & concentrating on the gas flow. i.e/ headwork, cams, tuned exhaust system etc, etc,

An SR20DET or 13B turbo is illegal, but if you're only planning to race it... Who cares, it's brown trouser time.

Personally - I've just completed a CA18DET into a '74 ute build & had my 1st couple of proper drives.
Being a motorbike bloke, I was a bit sceptical about what to expect in terms of performance. BUT - 1st time I got well & truly into it, the whole thing kicked sideways, both rears lit up.... all hell broke loose.
Afterwards - I was grinning like an idiot for days.
Motorbikes.... What are they?

This is all with std ECU & a T28.

As someone else said, there's a reason so many people are doing this conversion.
Go CA18 turbo.... Trust me, you won't be dissapointed.

Have fun,

Coops