The traditional class rifle rules for the ASSRA, ISSA and WSU, all have a technology cut-off date of 1917. That is, if a particular technology or device was available prior to that year, it is allowed. 
I do not think front sights attached with a mounting block like the Redfield Olympic were available pre-1917. If you have published evidence such as a catalog (or copy thereof) showing that front mounting system was in use prior to the cut-off year, you would be good-to-go.
It would probably be helpful if you want to shoot in a traditional class, to familiarize yourself with those rules. Each organization has them available for download on their respective web sites.
Hope that helps.

GeorgeC
As I recall, the traditional rifle rules were adopted at the 1995 or 96 ISSA Schuetzenfest. I was working on my master's program at the time and did not attend that year. There have been several revisions over time. That set of traditional rules was subsequently adopted by the ASSRA and WSU almost verbatim. 
If you have not already done so, my suggestion is to familiarize yourself with the basic set of rules for the ASSRA, ISSA, and WSU, then read the traditional rules for each organization. I think the traditional rules will make more sense in that context.
Here is the section from the ISSA traditional rules that deals with sights and sleds.
2. Technology cutoff of circa 1917 as regards patents, sights, cartridges, loading techniques, and general configuration of the Schuetzen rifle. No modern block-style or wide-bottom forearms. Old-style muzzle rest “feet” are allowed, but must be attached to the barrel. No modern Olympic-style sights, rear iron sight diopters, adjustable buttplates, plastic sight inserts, or “Bloop tubes”. No machine rests. (For clarification a machine rest is any one-piece rest that supports the rifle at two points and allows the rifle to be mechanically adjusted, incrementally, front and back, for windage and elevation.)

Dimensions for a barrel sled were established at 6" wide, 1.5" deep and 3" high I think (I have yet to find my note on that). It was necessary to set limits on sleds as someone showed up for a match with a sled that weighed about 20 pounds, or so I've been told.
It is pretty well accepted that a front sight needs to be in a barrel dovetail. I am not aware if anyone has ever challenged that point.
As to there not being any rules governing a front rest, that's not exactly a fact. There is the spirit of the game. If a shooter tried to use some digitally controlled hydraulic wiz-bang front rest, my guess is the local Schuetzenmeister would request such a device be removed from the firing line.

I don't shoot ISSA.  The ASSRA rule book does not say that a rifle has to have a dovetail sight.  "Olympic type sights" is very broad.  Just because the sight is named Olympic means it is not an olympic type sight with adjustable iris, etc.   
You still didn't address my reference about the bench rest (not the sled).  I consider the sled and a bench rest two separate pieces of equipment. A modern bench rest would not be in the spirit of before 1917 rules, but there are no rules governing say a Sinclair bench rest with cables and such.   
Would a Lyman Model 93 be legal?   
Please take my discussion in a positive note. I am surprised that no one else has joined in this discussion.  BTW, I have studied the rules and they are very subjective.

GeorgeC 

Three examples. Which is legal?

I agree that they are subjective.    lets face it,   very few of the "original" schutzen-type shooter used a bench rest for anything but developmental work.   There WERE some actual what could be called bench rest matches in several forms, but schuetzen was predicated on offhand competition.

Our modern ASSRA competition is somewhat of a bridging effort between bench rest and more traditional offhand with the "traditional-CLASS" rifles thrown into the mix---more or less to suit the "purists" who enjoy shooting their original classic era rifles (and more power to them).
  As a result IF you are shooting with a self-designated "Traditional class" rifle the identifiers are basically the semi-arbitrary pre-1917 American classic single shot rifles and appropriate sights. 

  For the most part bench equipment is only what is legal in the general rules for all ASSRA competition.   I'm not sure there any rules at all that apply to the actual bench-rest design or mechanism for the bench rest competition.  So you could theoretically bring your electro-hydraulic worm gear bench-rest with the  micro-processor controls and still shoot a rifle that is "traditional-class" ----  but mind you no laser sights, down-range electronics or adjustable tuners    Have fun!!!

QM. I refer you to page 5 of a post on sleds.

(You need to Login or Register to view media files and links)

Thanks Randy.  I assume you are looking at the photos on your phone, so from my computer perspective would the upper right be the 1st or 2nd photo?  The first being a Redfield that fits on a base, the 2nd fits in a dovetail, the 3rd fits on a base. I just hate to have a dovetail cut in two barrels if I don't have to.   
My other issue is that the parameters of a sled have to be such close tolerances when any kind of bench rest can be used.  I hope you don't think I am nitpicking, but that is JMHO.  BTW, I really like your bench set-up.
GeorgeC