Here are some thoughts for you.  Usually when you have a cheese where the curds don't knit well, the problem of reaching temperature too quickly during the “cooking” process is the problem.  BUT – from what you are saying, that is something you were very careful about. 

Judging from what you’re writing, and being familiar with the recipe I think you used, there is one item that isn’t very clear in that recipe that will affect how your curds knit:

-If following the “Home Cheesemaking” recipe (Ricki Carrol), after draining the curds (step 7) they will be a bit “matted together”.  Before adding the salt, gently break the curds up with your (very clean) fingers so that they are about the size of quarters or a bit smaller.  When adding the salt, sprinkle it over the broken up curds and mix it in lightly with your (very clean) hands to distribute the salt throughout the curds.  Then proceed to step 8, allowing them to rest at 95 for 30 min.

If the curds aren’t broken into relatively uniform size at this step, what you have is a huge hunk of curds that don’t have the salt evenly distributed which can also result in uneven draining of the curds and the condition you described in your original post with the cheese staying in “hunks” and not knitting together properly.

Some other things to note – You mentioned that you’ve seen another recipe you might consider using and some questions regarding weight when pressing.  When making queso fresco I also had a different recipe that is almost the same but with a few differences that I follow that have been very helpful.  If you would like, I can send that recipe to you in PM.

You mentioned press weight – Yes, this CAN make a difference in how the cheese knits and it is one of the major changes that I utilize when making queso fresco.  If you press at too high a weight initially (for any cheese), it also can cause the curds to seal in such a way that not all the whey can get out resulting in poor knitting and a sour cheese.  When pressing, here are the steps I use:

10 lb for 10 min.  Remove from press, unwrap cheesecloth, flip cheese over, rewrap w/cheesecloth and return to press.

20 lb. for 1 hr.  Flip, rewrap, & return to press (as before).

35 lbs for 6 hours

(These weights assume a 4.5” mold; weights differ depending on diameter of mold)

If you press gradually like stated above, it is not necessary to worry about letting the temperature of the curds to be at 70 degrees.  (Also, depending on the cheese, letting the temp. drop that low before pressing can cause other problems.) 

There are several other things that I do differently than the “Home Cheesemaking” recipe that I think help this cheese be more successful.  These changes are small, but have good results regularly.  Let me know if you’d like those and I’ll send them!

I will need to get that to you tomorrow as I'll be away from computer tonight.