Not sure what's going on with my two M1s--any help would be appreciated!

I borrowed a friend's timing block (one of those plastic ones from Brownell's, been thinking about getting one), and it fails to release the bolt on either of my rifles.  However, a fully loaded clip (with dummy rounds) works just fine.  I've never checked the timing on these rifles before, but I find it hard to believe that both are bad, which implies the timing block isn't big enough.

So, what do I do--assume the timing block is crap and find a better one (I've seen the all-steel versions out there), or replace two bullet guides for starters and go from there?

Timing gages are used to help diagnose rifles with problems and for IDing rifles that may have problems.
Since your rifles are working properly, there's no real reason to gage them.

In this case I'd tend to think either the gage is worn or was no good from the get-go.

In any case, why start replacing parts on rifles that are working fine.
I'd test fire the rifles, and if they work OK, I wouldn't worry about it until there was a good reason to.

Well, that's just it--I just picked up one of the two from a private sale and I wanted to make sure things are safe to shoot. I wanted to do a timing and headspace check before I took it out to the range.  After it failed the timing check I figured I'd try it on my other Garand, which I know works, but then it failed too.  What's interesting is the timing block is basically brand new.