Is this an okay way to mount gantry to linear bearings?

[PaisleyPCdoctor]

I think I'd be more inclined to use more smaller fasteners instead of 3 M8's, that way you should get a more evenly distributed/less distorted and stronger join between the parts.
I'd probably go for a row of M5, or maybe M6.

I'll put some thought into that. My thinking for 3 m8 was as an adjustment/shimming point when I get to tramming stage, but I think you're right. Thanks.