Your converted 1911 was probably done in the 1960's, as were many. 7.5x55 is a .308 caliber. Most are marked on the barrel and the magazine with " .308 ".
Best to take pictures and continue to ask more at gunboards, surplusrifle, or swissrifles forum. If interested, there is a D&T scope mount for your rifle. Replacement sights ( iron ) will be difficult, not impossible, to find. My 1911 has Ross rifle " Sergeant peeps " as an improvement. There is quite a bit of info on the 'net. Hawkster318 has a section on these converted rifles on his website.