There are some real ironman nerds on this forum so we have documented and noticed far more details than are probably necessary. the truth is, your frame looks like a nicely built tange 1 frame from around 1986 with shimano 600, which is exactly what a centurion ironman is. the geometry may be different, or it may be exactly the same.. and if so, it will probably ride just like one.

in some ways its much cooler as IM sold so well that they are all over the place. your bike is much rarer :_)