I could see one of those real mixed bag type of defense forces coming out of this.
I could see the army with maybe some SOKO built Gazelles and maybe some SAAB stuff coming in for the air force.
This, of course, would not preclude use of Soviet or Czechoslovak built gear if it was desired.
If you really wanted to play with the scenario a bit more, suppose the Austrian State Treaty of 1955 had been more lenient with regards to armaments. Under the treaty conditions, Austria could not effectively defend its airspace due to treaty regulations which limited Austrian aircraft to guns only.
A more lenient 1955 Austrian State Treaty in combination with a successful 1956 Hungarian Revolution and the degraded state of relations between Yugoslavia and the USSR in the 1950s could have opened the door to a tri-national defense agreement between Austria, Hungary and Yugoslavia. The historically close connections between Austria and Hungary would certainly aid in such an arrangement.
More lenient conditions in the 1955 treaty would likely have seen Austria take a serious fighter aircraft much sooner than they did. In the real timeline, they took second hand Saab 29s in the early 1960s and only took second hand Drakens in the mid 1980s.
1956 was when Yugoslavia took delivery of their fleet of Canadair Mk.4 Sabres; as such, a tri-national defense agreement precipitated in part by a successful Hungarian Revolution would be quite conveniently placed in a WHIFF timeline for both Austria and Hungary to get in on the same Sabre deal.
Presuming relations between Yugoslavia and the USSR do not get patched up in the 1960s, we'd see the three countries go shopping for a new fighter by the early to mid 1960s.
Realistically, I think they'd most likely get a load of F-104s and F-5s from Canadair as a lot of European countries did and end up with the F-16 or F/A-18 as a replacement.
From a WHIFF standpoint, Let's say SOKO gets a license to build Drakens for the three countries and that holds them for a respectable amount of time with respect to air defense. We all know, in a perfect world, the Saab Viggen did not get embargoed.
The three countries would most certainly have the SOKO G-2 Galeb as their standard jet trainer and it's single seat J-21 Jastreb variant for light attack. Logically, the G-4 Super Galeb would begin replacing them through the 1980s.
From the standpoint of light transport and utility, I think the Let L-410 Turbolet would not be out of the question.
Larger tactical transport would most likely come in the form of the C-160 Transall or the C-130 Hercules.
I'll stop there and go take a cold shower as I've worked myself up a bit.