General consensus is that AE86 front brakes work good - but I don't have personal experience in them.
If you are going to convert to coil over then get a RT13# struts, add a pair of LN10# Hilux/Pickup 4 spot callipers over a Peugeot vented disc (machined down by 5mm and converted to 4 stud). A friend has done this to his RA23 and it is excellent. Convert the RT13# strut to coil over or just leave it stock with aftermarket RT13# springs.
A complete MX73 strut and front brakes end fits easily for a modest increase in braking power from a larger vented disc (but not as large as the Peugeot vented disc).
Use RA2# steering knuckles (most Toyota knuckles do not bend inwards and so the steering rods are too short and the bolt pattern is different on most other Toyota knuckles).
Rear brakes:
On your trip to Japan you might be able to find an RA25 GT or RA28 GT rear end.
This has the same brakes but has an F series diff and the complete housing is a direct replacement on your '73.
Note, F series diff does not fit any other A2# Celica housing.
Hilux N2# rear end has 10" drums (Celica has 9") and a super strong (and heavy) G series diff.
You will need to relocate the suspension mounts.
Similar for the Landcruiser rear end, except you also need to shorten one side.
A Skyline (circa 1985) rear end has disc brakes, a strong diff and the same bolt pattern as your current wheels.
You also need to shorten one side.
On my RA28 I used a JDM spec MA45 Celica XX rear end with disc brakes and LSD.
Mine only came with the T series diff but other Celica XX/Supra rear ends have the stronger F series diff.
Slightly wider than the A2# rear, so you might have to flare and roll the wheel arches depending on your wheel size (I flared and rolled mine to suit Soarer 15x6" rims with 225 tyres).
You will need to relocate the suspension mounts.
The AE86 rear end fits.
Gives you disc brakes.
You will need to relocate the suspension mounts.
Axles have a habit of breaking if you increase HP.
Disc brake axles are different to drum brake axles, so you will have trouble replacing them in America.
Only has the lowly T series diff.
Crown (circa early/mid 1980's?) rear end has F series diff and disc brakes.
You will need to relocate the suspension mounts.
These have 5 wheel studs but that suits the front 5 stud Peugeot vented disc.
Personally, I would leave the rear brakes alone as the 9" drums are quite good.
Just upgrade the fronts - which are not very good.
Haven't found an IRS that fits the 2# Celica's narrow rear chassis rails without a lot of effort (eg building new rails).
Master cylinder is easy to upgrade to a Hilux, Corona, Cressida or Crown 15/16" MC to give a stiffer pedal for better control.
- Stepho