If you want to EFI it later down the track then thinking ahead I would just use a locked up electronic dizzy. Then when you're ready to fit the efi, its just a matter of hooking the elec dizzy up to the ECU as the ignition input, because this input will also need to be a constant pulse, ie locked.
The reason I asked if you want to fit a cam is if you're talking a/r ratios already then you should factor the cam you plan on using into your decision.
A .48 housing will nearly have the response of a S/C, and just like the S/C it'll start to run out of legs in the top end. For this reason you would want to combine this with a very mild or even stock cam.
Now on the other end of the scale if you want to run a .64 you need to combine it with a cam that will work in much the same rpm range. When I was running a .64 T28 (S14) boost didn't come on until around 1000rpm later, but when it did it just kept pulling harder and harder the more you reved it..... which worked a lot better with my larger cam than what my T25G does.
Put it this way, with the T25G I hardly ever see the shift light as I'm better off cracking another gear and using the mid range. With the T28 I would quite often see the shift light and sometimes also find the limiter set at 7500.