Engine mount arm question 84 300 SD

[dannyF]

I managed to get the engine mount arm removed - will give details later, was a bit challenging for me, but do-able.

Anyway, my question is that when I drilled out the screw that supports the engine mount into the arm, I had inadvertently drilled into the screw hole such that a portion of the hole was drilled into. That is, there are threads for about 1/2 of each turn. I already knew this and it was the reason I removed the engine mount arm. However, surprisingly, now that I removed the old screw remnants, my new allen head screw seems to fit fine! So, can I go with this, or, must I now assume that the old system is compromised and that I need to drill all the way through and get a longer bolt supported by nuts at the end? My temptation is not to drill into the engine mount arm and to use the old system, but I will drill it out if safety is compromised.