That old stone appears to be a Norton "combination" Crystolon. If so flattening on concrete would take forever, and include a good chance of breaking the stone. If you want to save it you should probably get a mason to lap it flat for you. But since new ones cost $18 for the 6" length, and $20 for the 8" length, it's not really worth it.
The stone flattening equipment on the page Koko linked is for water stones, not oil stones and would not do the job.
Anything finer than 3K JIS or "Translucent Arkansas" for Wusthofs is a waste of time.
When it comes to synthetic oil stones, Norton India stones are better than Norton Crystolon, but Razor Edge (8x3, Coarse and Ultra-fine, $65 the pair) are the best.
This is the set I use for soft steel knives:
- Norton IB-8 ($20 8" x 1" combination India with Coarse India surface for profile and repair, and fine India surface for drawing the first burr);
- Norton IM-50 Sharpening Station for holding the IB-8 ($15)
- Hall's Soft Arkansas for refining the burr ($29); and
- Hall's Surgical Black Arkansas ($84) for finishing and polishing the edge.
You could do worse.
You don't need a $180, 11-1/2" Norton tri-hone. 8" stones are perfect for a home sharpening kit. If you decide to get Arkansas stones, remember that the quarry counts for a lot. Hall's is either equal to the best or the best for all four grades (soft, hard, black, translucent). You could save $42 by going with the $71 combi Soft/Black instead of the separates.
Try to remember that grit numbers do not translate from one system to one another, and for that matter grit numbers within the same system aren't consistent from manufacturer to manufacturer and sometimes not even from one line to another. Even terms like "coarse," "medium" and "fine" don't translate particularly well. Any chart you see comparing Arkansas stones (and many other natural stones) to particular grit synthetic stones is going to be extremely misleading.
If you have questions, ask. Don't rely on retailers' or manufacturers' descriptions.
Edited by boar_d_laze - 6/7/13 at 3:31pm