You should have your magnetos cleaned and adjusted by a pro.  If you have the skills you may do this yourself tho it may blow your engine warranty.
Should you somehow lose pressure to a mag at high altitude a dirty mag won't perform to specs.  Sparks will fly and it won't be pretty.  That's why there are two independant spark supplies on aircraft engines.
Unison has made Slick the best and most simple mag to date.  How does your engine run at power and altitude on a single mag?  Have you done a high and low mag check?   It would seem many take the spark supply for granted.
The TSIO-550 is one of the hardest piston engines to work on (well, it's not a GIO Lyc. on an old 580 Commander, or, worse yet the GSIO Queen-Air), mags being the worst and hardest to get at.  Pulling the top aftmost plugs is only a start; a vain attempt to keep the engine up to snuff.  Have you yet broken the torque seal paint blob applied by Continental which shows if your mag has been adjusted?  Was it looking towards hell from there?  A maximum of two degrees off specified timing is way too much and yet many of us will live with that just to avoid the deep involvement of removing and re-working these mags.
Don't be a slouch.  Go in there and take the time.
Start by pulling the #1 bottom plug and find TDC by feeling the compression. There is no timing mark as you have found.  Something about liability law...
Set TDC by feeling with a very thin screwdriver for the piston and rock back and forth untill you get it up.  Note the prop position.  You may now enjoy the happiness of mag removal and maintenance.  A big rubber mallett may be required.  That's how long your mags have been neglected.
The advanced spark position assumes the impulse coupling is released.  Don't spark the mag unless there is continuity to the plugs or the "P" lead is grounded.  Internal sparks only hurt.
Purchase the Unison Master Service Manual from:
                                                                               Unison Industries
                                                                               530 Blackhawk Park Avenue
                                                                               Rockford, IL   61104  USA
Anyone who can build a Lancair will have no problem understanding the Unison book.  The timing tool "T-150" timing guage and the timing pin are necessary as well as a torquing screwdriver.  Torque specs are in Table Five: service limits.  Cam grease is available from Unison.
Don't turn the prop untill the timing pin has been removed...
WPD  s/n LVP 449