TR6 Timing Cover Screws?

[levilevi@home.com]

Listers,

Is there a good reason TR used bolts with a screw type head on part of
the TR6 timing cover and hex head bolts and nuts on other parts of the
cover?  Any problems that'd I'd create by replacing the screw head types
with hex head bolts?  Using the proper lengths in the appropriate holes
of course.  

Thanks
Bud