Tough call... You sound like you know what you are doing so I may be an amatuer giving advice here but when doing a timing chain a bit of coolant does fall into the oilpan and it doesn't take much water to make it look milkshake-ish. Scared the living crap out of me last time. I'd do a compression check, look at the plugs, and get my antifreeze tested before I went switching blocks. And if you drove it for that short of a time and it didn't overheat at all, I'd guess that you are fine anyway, even if you need a headgasket. If you don't feel like testing, and have another block, slap a headgasket in it and run it until it throws a rod, then slap the other block in. Who knows, you may get another 100k miles out of the thing with an HG. I'd have to look it up but on Youtube I found a video of a 22re running still after throwing a rod.
throwing a rod and spewing all it's oil....