Hi guys, have not been on here for some time, found this thread and thought I may be able to contribute a little for you all.
Pictured is at top a Triace in .22 long it has a strengthened top strap, extended trigger guard flat as previously suggested and grip angle also as suggested.
Second down is in fact a 3 in 1, the grip has been hashed but is somewhat workable, it is pictured in .32cal, below is .22 long and below it .22 short fully ported and hosting a very short barrel length.
The lower barrels do not out of the box fit into a triace, sadly I may add.
The rear receiving cutout is different, not to say it can't be done but can't out the box be forced to fit.
The Triace pictured was in fact custom built for Alex Taransky, Australian Olympian of the late 60's early 70's hence the serial 810000, it hosts a lovely rolloff trigger and will shoot X ring everyday of the week with SK ammo.
The 3 in 1 has had a little rougher life, sad too say that when I found it unloved in Western Australia it was sexed up with new firing pins custom made by Alex and new buffer system fitted, it too shoots x tens all day long.
It's serials .32 802488, .22long 801612 and .22short 800565.
Both are a joy to shoot, sit well in the hand and short of busting firing pins are flawless, a recent State title shoot saw the trigger bar spring break on the triace, yep, you guessed it, no parts are available. Fortunately for me, Alex is a great friend as well as my coach / mentor and still has a host of triace parts so the triace lives on and continues to deliver.
If ever in South Australia, y'all may visit and compare side by side both models.
Hope this helps