If you have not found your solution yet I can give you some advice. The 2 bolts are normally 13mm (can use 1/2" also) but Briggs says some newer ones (after 00 date code, or 2000) have 12 mm. They thread into the side of the block through the hole in the flange on the side of the starter motor. The one bolt you can get at with a standard socket and extension. The second one is partially blocked by the starter shaft/bendix combination. The 'simple" solution (also Briggs recommended procedure) is to obtain a 1/4" drive x 13mm (or 1/2") swivel socket. When used with an extension and ratchet this is just small enough to fit in there and remove the bolt. Briggs sells for about $30, SnapOn sells for $39 or so, I assume Sears would have it, probably some hardware/home stores. Must be 1/4" drive, 3/8 drive is just a bit too large. Universal and socket combination will not work. Only other real option is to pull off shroud and flywheel to get at the bolt. Yes, it is a lousy design.
Now your question about the brushes. You will most likely be unable to get them back in place without totally disassembling the motor, but you are already 90% of the way there anyway. Once you get the starter dismounted you can pull off the back end cap and then remove the brush holder. While you have it open you can clean up the commutator and check the brushes. If the brushes and the bendix are bad just bite the bullet and buy a new starter. 16 tooth PLASTIC gear and 4.25" case length are the critical specs. There are a multitude of B&S part numbers that cross for this starter, but the model number for your engine would be 499521. Home Depot sells them for about $85, you can get a good one on eBay for about $50 delivered. There are some cheaper ones, but I have heard some bad reviews on them. To replace brush holder you have to push the brushes back into the holder and put some short sections of welding rod or small nails, hanger wire to hold them in place. Put brush holder back in place in the starter body and over the commutator on the armature, remove pins and brushes are back in place. Lightly grease the end of the armature shaft and the bushing in the end cap and put back into place. There is a video on YouTube that dragonslayer45895 posted showing the service procedure. It is 2 parts, kind of down and dirty, but gets the job done. The starter he is servicing has the new Bendix arrangement using the spring clip instead of the roll pin, but you will get the idea.
Regarding the Bendix. you can get a repair kit yet for the roll pin style. There are two types of kits, one with the starter clutch and one without. The clutch is the part closest to the motor and has a metal flange with two flat edges to it, The plastic helix it part of that. I would suggest that you spend the extra few dollars and get the clutch. That clutch is designed to slip if the plastic gear is overloaded and if it has slipped much at all in it's life it may be too weak. No sense in taking a chance for all the effort to remove and repair the starter. i assume you are probably missing the cage and spring off the end of the starter and the drive gear is staying fully extended and not engaging the ring gear. That is the common failure of that bendix design and I assume why they changed the design. if you buy a new starter it will have the new design, but is completely interchangeable with the old design. You can buy roll pin bendix repair kits from your local repair shop, online parts houses or eBay seller for about $15 or $20 delivered. Most will be Stens kit, as good as OEM IMHO. There are several YouTube videos showing how to replace the roll pin type bendix. My only suggestion is that you support the shaft when hammering the roll pin out and back in, not just rap on the unsupported shaft the way they do on the video. Risk of bending the shaft and/or damaging the bushing in the drive end cap. Part number for kit without clutch is 696539. Kit with clutch is 696540. Stens part # 150-118 and NAPA also sells the full kit #SME703443 for about $22, but they will probably have to order it in, most stores do not stock. Sears parts house also sells them, do not have part number at hand.
Suggest you check the valve lash before you put the engine back in service if you have not done it recently. A lot of starter problems on Briggs OHV engines (and other brands for that matter) is too much valve to rocker clearance. Should be .004" to .006" for both intake and exhaust on a Vanguard V-Twin. These engines have automatic decompression for ease of starting, but that valves will not open if the valve lash is to great (like even .010) thereby effectively disabling the function. This makes for very hard starting where the engine want to stall when it hits the top of the compression stroke. Puts a much greater load on the starter and can damage the plastic gear, damage brushes and overheat the windings of the stator and armature. Setting the valves is very easy to do as long as you have a set of feeler gauges. Again, several good videos on YouTube showing how to do it or you can refer to the B&S website.
Hope this helps if you are still working on this. If not, maybe can help someone else that comes here looking for answers.
