Interesting responses. I'm absolutely not disagreeing with anyone here as everyone seems experienced and knowledgeable. In all the B and RB builds I've put together I've shot for .0025" on the mains, but would have been comfortable up to .003". Being that I've never ran an engine as loose as .004 I have no experience to say it's a bad idea, but my concern would be oil pressure.

I'm currently assembling a 289 Ford. My mains are just shy of .0015" and it feels a bit tight to me although it's within factory spec. I'd be more comfortable with .002 on the smaller 289 journal.

Point being, old factory specs are much tighter than many of us like to run, even at a time when oil technology was inferior to what we have today.

To the topic starter, I would have recommended the .0025 bearing without hesitation, but it seems like you might be okay a little looser. Happy Racing!