Get out your "Machinery's Handbook". (as Hotater used to tell us all the time)
BSP thread pitch is the same TPI as NPT in only a few sizes, 1/2 & 3/4 share 14 tpi
1/16" & 1/8" pipe; npt is 27 , BSP is 28 tpi
1/4" & 3/8", NPT is 18, BSP is 19 tpi
I know that's close enough to jam it together, but it's messed up.
1" thru 2" is 11.5 & 11 tpi, but above 2" ntp uses 8 tpi, and BSP stays with 11 tpi.
Get out the thread pitch gauge and your copy of Machinery's. You'll be glad you did.
http://industrialpress.com/products/category_feature/MH
This link will give you an intro into what Machinery's Handbook is, and why you need it, as a Do It Yerself kinda guy.

So I bought a pair of glow plugs to mount in the COV plug.
They are for the VW 1.9 TDI mentioned above. NGK #5909 also known as Y-732J.
These are too short for the plug, which will have to be bored 3/4" at the square drive end if the tip of the glow plug is to stick out as depicted on the CMD site. This will need to be big enough to fit a deep well socket.
Also, the CMD glow plug ad shows a threaded stud with nut to make the electric connection, the 1.9 TDI uses a proprietary push on connection.  

I just blew the nose off my Chevy starter. When I didn't let up on the button soon enough, when engine must have sped ahead of the starter and over ran the starter gear and climbed it. Maybe my starter mount isn't stiff enough?
I really like your set up. Do you mind if we copy it??

Thanks for that DGman;
I can report on the air preheater. I installed it when I got home from work, and wired it up...temporarily.
It seems to have assisted with starting, but not with the governor side cylinder, so I need to look into something there. It certainly has plenty of compression when rolling it over by hand.
So I rolled it over on the starter until I showed good oil pressure pulsations, then touched the preheater wire to the battery for about 8-10 seconds, then hit the starter and dropped the compression release on the Gov side cylinder. It smoked, but no thrust.
I dropped the release on the second cylinder and it took right off. And blew the nose case off the chevy starter! 
I guess I didn't release the starter button soon enough. 

Well it's been 3 years...
But I finally installed the air preheat in the intake Y manifold of my Ashwamegh 25/2. the preheater is for a Perkins diesel, as used in a Massey Ferguson diesel tractor, probably the most common in the world.
I originally planned to use the elbow manifold that bolts to it and holds the air filter, but the air passage was too small. With the air preheater element (glow plug) in there, I felt the air flow would be restricted.
I just mounted the manifold in the drill press, and drilled the 13/16" tap drill size in 3 steps. Then tapped the hole (7/8-14) right in the drill press to make sure the hole is straight.
The intake Y manifold has a thick flat pad on the bottom, enough to drill and tap, it will be strong enough.
I think I'll just get a big push button switch to energize it, and wire it to the battery supply to the starter. Then I can push the glow plug button for about 10 seconds, then push the starter button.
I'm still waiting for someone to tell us what glow plug part number is the perfect size for the COV plugs.  
I've been very patient, but I'm getting some free 6.2 Chevy glow plugs in a few days, so we'll see if they are a possible fit...

I made up a plexiglass window for my 25/2. It's the best way to see what's going on in there.
Back then we were talking about internal oil filters, and how much oil is splashed around by the dippers (A Lot!!). That lead to the Hotater trap filter, of which I have a variant.
Unfortunately, I made my filter basket too wide, and the dipstick won't fit. Now I take the crankcase door off just to check the oil, so hand pre-lubing with an oil can, and internal inspections are a regular event for me.
I like your fittings, I did a similar job when I plumbed up the oil pump discharge, out thru the crankcase to be heated and filtered, then back in to the distribution manifold.
These engines are the best for experimental tinkerers like us. 

Time to run your standby generators, and get any last minute repairs or upgrades done.
Storm season is upon us, and last year was a doozie. Then winter follows. When you are snowed in is not a good time to find out your genny won't run, and you're out of food. 
I just inspected, pre-lubed and ran the 25/2, so my primary generator is all set. I've got some semi-portable Onan twins for back up and loaner to Mom etc. They get the service and test run next...
Don't forget to stock up on food, meds, stove fuel, or whatever you need in your life / location.