Stock-sized U-joints wanted

Ouch! Before fitting a new u-joint, very carefully check the bore of the holder that lost the cap. All u-joint caps are a standard diameter- the same on all parts of that series within a couple of tenths (0.0001"). So if the press-fit cap and/or snap-ring are loose in a holder, you will likely have the same results with another brand. It also means that metal is missing, displaced or the holder is cracked, so substituting Lock-Tite or softer metal shims won't work for long, either. You're routing some 200 ft-lbs of torque (ca 400 total) directly through both half-shafts.
If the cap is tight but the snap-ring doesn't fit, its possible for a machinist to deepen the slot for the snap-ring, and you can assemble it such that the rounded edge is facing inboard. This positions the sharp(er) edge of the snap-ring against the outside where it may tend to dig in & hold a little better. But it may be you simply need a new u-joint holder- which means a new half-shaft, as the parts are not normally separately available.

Thank you for the reply. W/o taking precise measurements, I believe that 1) the aftermarket joint is ever-so-slightly longer than stock, from face-to-face at the caps, or 2) the aftermarket clips are thicker than stock. I have a feeling that #2 is more correct, I envision the manufacturer built the joint to stock specs then just threw standard clips into the package. This, along w/ rust in the clip groove, is what I think did not allow the clip to seat fully. When replacing I filed down the clips, which does not sit well w/ me. Now I have better-seated clips that are weaker. Machining out the grooves seems like a good option.