I need some help with a Long Branch

I don’t think this is correct. The threads on the bolt for the bolt head are different, and are recessed into the end of the bolt body for the No. 4.  The length of the long rib lug is different. The distance between the long lug and bolt handle is different.  I was not able to lock a No. 1 bolt body into my No. 4 just like the OP found. 

Thanks very much for some pertinent ammunition information!  I was actually looking at some inexpensive Ishapore ammunition until you posted this.  I'd rather find spent casings, prime them with good primers, then load them with the IMR.  I used to have a Lyman and a Hornaday loading manual from the early '70s.  I'm sure they'll have some loads.

My goal is to stay well above "Squib" level and well below "Max-Pressure" level so as not to stress my Long Branch.

^^^^^  THIS

And, you can get current load data online.  The Hodgdon website lists load data all the powders they distribute, including IMR, Winchester, Accurate and Ramshot.  Most all powder manufacturers have a website with rifle load data. 

   

Do not try to fire the rifle until the new bolt has been properly lapped in to the lugs in the receiver.

I built myself a somewhat crude but effective machine to accomplish that task, but it can be done by hand.  Put a fired case in the chamber and find a coil spring about the same diameter as the bolt or a little smaller.  I use a piece of plastic inserted into the bolt body threads a guide for the spring.  The purpose of the spring is to provide equal backward thrust on the bolt while by hand you work the lever up and down until the lapping compound you put on the recoil lugs shows that the contact on all four surfaces is even and as large as it can be.  My machine does the up and down part for me.

After the bolt is lapped in, HS gauges will be needed also.  Lap the bolt head face on a suitable flat with emery paper, then fit and test the squareness of the bolt face to the rear face of the no-go HS gauge with blue or a permanent marker etc.   You need full, even contact across the face of the bolt and the face of the HS gauge.  This will show whether the bolt head is square to the chamber.

The bolt head should not turn past the long recoil lug more than 12 degrees, but of course there is some leeway in that, depending on how effective you want your primary (as the bolt handle is lifted) extraction to be.