The SLR-100H receivers were Arsenal of Bulgaria made, and they were sold here through the Intrac Company. Intrac sold them in two ways....one way was selling just the receivers......and the other way was to build some up as complete AK's and barreled actions using used surplus Hungarian AK parts kits.
The built up guns were not done by the Intrac people themselves, but rather Intrac contracted outside firms to do the builds for them (which is an Intrac normal procedure). A few companies that I know were contracted to build the SLR-100H AK's for Intrac, were the Gordon Technologies firm, Ohio Ordnance firm, and Blue Ridge Precision. I believe there was at least one more on that list (just can't remember which ones). The thing is, they also sold quite a few of the SLR-100H receivers as stand alone items. These were to be built by other companies and private individuals.
What leads me to believe your gun was not a complete Intrac offered SLR-100H gun, is that you mentioned that some parts are blued, while others are phosphated. If the gun is a 100% Intrac offering, it should all be one finish (like the phosphate, which I believe was the standard for that Intrac offering). If you remove the lower handguard and find the letter G stamped into the right side of the barrel, it will be a Gordon Tech build, which was one of the companies contracted to build complete SLR-100's for Intrac. There would be other tell tale markings on the receiver or in some other place on the gun that would prove the gun was built by one of Intrac's outside builders (that is "if" indeed it is a complete Intrac offering). The fact that you found no other markings beyond that of Intrac's, is another clue that it probably is not a complete Intrac offering.
You definetly have an Intrac SLR-100 Bulgarian receivered gun, but not sure if the whole gun was an Intrac offering, or a gun built up by someone else using the Intrac receiver. The SLR-100 receivers started life in Bulgaria as 5.56/.223 milled receivers that were originally intended to be made into a new Arsenal USA offering. It was a project that fell through because of BATF regulation changes here in the U.S.
You see, Arsenal USA was planning to offer a 5.56/.223 version of the SLR-95, but then the foreign made thumbhole stock guns were also banned from importation.
Later, the receivers were modified for 7.62x39 use, and purchased and imported in by the Intrac firm.
Whats kinda funny is that Arsenal USA ran out of SSR-99 receivers at one point towards the end of that models production run, and Arsenal USA ended up buying some of these Intrac SLR-100 receivers to finish their projects. So some of these receivers that were originally destined to be Arsenal USA products, ended up being just that ;) While some SSR-99's were built using these SLR-100 receivers, the actual legal model designation had to be listed as SLR-100 because that was the receivers designation.
Hope this helps a bit :)
PS. While I don't know what the quality of your guns build is, I do know that you have a top of the line forged, milled, and heat treated Bulgarian receiver :)