[PercentSevenC]

There are four ways to mount a 13B in a 12A chassis. All require a 12A or GSL-SE front cover (tapped for turbo oil return, in your case).

1. GSL-SE crossmember (probably difficult to come by if you're in Japan)
2. Racing Beat front mount bar
3. Slot the holes on your 12A crossmember and front mount bar each by 10mm
4. ReSpeed's adjustable crossmember (if you're planning on converting to rack and pinion steering)

Ditch the stock ECU. If your budget is tight, get a MegaSquirt. Then convert the twins to non-sequential or go single.

Like TehMonkay says, get some sticky tires and good brakes. I'd recommend ReSpeed's FC brake conversion. Don't forget a nice clutch/flywheel setup. Get an aluminum radiator and front-mount oil cooler and intercooler if you don't have them yet.

If you have an '84-85 (big flange, big bearing) rear end, you can just get the Moser axles from ReSpeed and it should hold as long as you're not making crazy power and launching on slicks. I'd be more concerned about the tranny. Upgrading to a TII unit would be a wise investment, and allows the use of 240mm cluch components.

One crucial step is an upgraded fuel system. Simply sticking a Walbro 255 in the stock system will not do. You'll need a surge tank at least. Tweakit sells them. Depending on your planned power level, and whether the car is a 12AT model or not, you may need larger lines as well.