Don't think it's a problem being it's been many, many years street/strip and after the last freshon up 11 years ago, it still looked and worked great. LOTS of wives tales out there.....  My 575" hemi and my wedge both have solid rollers and stock timing covers. No issues. On the distributor collar issue...if the gear moving up and down won't affect timing, then why does the timing get much steadier after installing the collar? Is something else going on here? I've done this on both of my own engines and the timing most definitely does not move around nearly much w/ the collar on the distributor from my experience.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
| 
