Dave - you don't need to go tearing your 125 apart to find out what you need for studs and spacers, and it doesn't hardly matter about being a narrow frame. The studs and spacers were used on the K engines in the 1x8/9 series too. I don't know what parts look up you're using. When I look at the CCC one linked here I see it shows requiring 6 (six) hex head mach screws 3/8-16 x 2 1/4 (this is listed under the head info). My parts book is only for wide frames and for the K engine in the 128 it shows requiring
5 (five) studs Kohler Part No. KH-237277,
4 (four) hex head cap screws that are 3/8-16 x 1 1/2 Grade 8 (alot short than yours),
4 (four) spacers KH-X-400-71,
5 (five) hex head nuts 3/8-16,
5 (five) hex head jam nuts 3/8-16
It's sure odd my parts book shows the cap screws being 1 1/2 (for the engine in the 128) and the CCC site is showing 2 1/4 (for the engine in a 126) but I'll bet both will work.
I'm hoping Lewis will pipe in after he gets home from church
, or maybe someone else has an engine open that can give exact details.
You can also do a little more detective work. It's obvious the threading on the studs will be the same as the bolts so that's one answer. Next if you look at Lewis' pics you can see how much area the spacer take up - and that they come up just to the top or are slightly above the tin cover. Since the nuts should be the same thickness as the heads on the bolts I think you can determine how large the spacers should be.
Now - the next question on the studs - requires a little more guessing. My recollection is the studs do not have stops (blank threaded areas). I don't think they can have stops since you have to install a washer and nut to torque the head, and then you add the spacer. (If they had a stop it would have to be less than the thickness of the washer and I just don't think they have stops). I believe you just install the studs until they bottom out. So, with this in mind you could see what you have laying around and handy to try - something with the same threads about 3 or 4 inches long, and screw it in all the holes to see how much thread depth you have, and then you can calculate back from that to determine the stud length you need.
(Also, I'm suggesting you check all 9 holes just to verify how much threaded area is there on every one).
One other thing - I mentioned my recollection was the studs are installed until they bottom out - if you are installing the L shaped engine hanger bracket on top of the heat shield you need to leave that stud about 1/4 in from bottoming out.
Now - it's taking me about 30 minutes to type all this up. I wonder when someone is going to give us the actual lengths of the studs and spacers.