There's a Provisional Edition (6/69) shop manual on ebay for $1499.99.  In an earlier thread dating back about 4 years ago, a Provisional Edition was listed for $1024.
 
http://cb750sandcastonly.com/smf_forum/index.php?topic=393.0

I'm not sure if this is the same copy or not. 

http://www.ebay.com/itm/1969-69-1970-HONDA-SANDCAST-CB750-K0-PROVISIONAL-PROTOTYPE-SERVICE-SHOP-MANUAL-/161649692947?hash=item25a3129113&vxp=mtr

Sandcast 4286 is listed on ebay with E371.  Seller says he acquired the bike with a K1 engine and put in E371.  In the VIN directory, 4286 is listed with E4991.

It looks like a very nice restoration.

http://www.ebay.com/itm/Honda-CB-/331539934633?forcerrptr=true&hash=item4d3151eda9&item=331539934633

Hi there. My name is Kevin and I live in Lubbock, Texas. I grew up in southern California and I bought my first CB750 in 1972. I was 17 at the time and fresh out of high school. It was a brand new K2 in Sunrise Flake Orange. Later I bought a Freedom Green K4 and then a used Candy Ruby Red K1 (which I still have).

Fast forward 42 years...  A year or so ago I stumbled across a sandcast on the Santa Barbara Craigslist. It was in very decent shape with only 10K miles and the gentleman was asking $10,900.  I ended up paying $12,000 for it when he threw in a brand new set of HM300 pipes (still in the box). If the pipes are worth a ridiculous $3K in today's market, I figure I paid about $9K for the bike, plus the travel cost to CA and back.

The bike (2293/E2456) was last registered in CA in 1998 and it's got most of the sandcast parts. It's had a rattle-can paint job that will have to be redone - but it's not too bad for now. The tank is very clean inside but it's not a wrinkle tank. The seat has been recovered and it looks really bad - but the original pan is in good shape. It's also missing the recessed ignition, the mirrors are not original, the oil filter case is finned, the side cover emblems don't match (one black and one gold and they are both mounted backward). Haven't taken the airbox out yet - so I don't know if it is cracked. As for the exhaust, the bike has a set of Bassani four-into-two pipes. I can replace them with the new paragraph HM300's that I have - but I think I'll opt for a set of Yamiya no-number exhaust and put the HM300's on my K1. On the plus side, the chrome is in really good condition for it's age and there is very little rust. Same with the engine. It's got a really nice patina and there is very little corrosion.  It turns over but I haven't started it yet - so we'll see what happens.

Right now I'm working on restoring a K2 and K5 and fixing up my old K1- so it might be a while before I get around to working on this one. When I do, I'm sure I'll have lots of questions. The knowledge-base on this forum is incredible!

Kevin