Just a little confused here. Just exactly what does your combined overall length have to do with your velocity or pressure or the phase of the moon??
In your particulars, your combined overall length will be completely governed by the length of the Carrier Block in your '73. You will achieve correct OAL simply by crimping into the crimp groove for any bullets you describe.
For finding a load, other than what are called cowboy loads, READ THE MANUALS. There exist a plethora of load data well within SAAMI limits for the 45 colt round. ANY load you find published in reloading manuals are within SAAMI recommendation unless specifically listed for Ruger or TC. And the data flagged for "Ruger" is intended for the original sized Rugers. NOT the "New Vaquero"
It's unfortunate you don't wish to deal with the cleanup of BP. Dealing with the cleanup of BP in cartridge guns is actually easer than dealing with smokeless cleanup. The difference is simply, you HAVE to cleanup after BP.
All of which brings me to a final thought. So far, you have found fault with everything suggested. Which leads me to believe you are either playing Devil's Advocate or your just TROLLING. Are you just a TROLL??
Not sure who you're addressing here....
Cartridge overall length definitely affects pressures and subsequently velocities; not how much of the bullet is out of the case, but how much is IN the case. The deeper a bullet is seated in a case, the less space there is for expanding gas from the burned powder, which increases pressure, which increases velocity.
Because most .45 caliber lead bullets, were designed to be loaded in revolvers, their crimp grooves are too far back to permit a cartridge length (<1.6") that will function in a '66 or '73 lever rifle. The Lee bullets I illustrated are an exception. The bullet original to the 45 Colt will also work, but it has no crimp groove and will likely telescope back in the case unless it's seated on top of a charge of powder such as black powder or a super slow burning smokeless powder.
Manuals are a great source of reference, but most of the data therein is developed in special test equipment such as universal receivers with longer than standard barrels. For their .357 Magnum, .44 Special and 45 Colt data, Hodgdon used 10", 8" and 7.25" barrels, respectively. As a result, velocities are rarely close to those in actual revolvers and a chronograph has bore this out for me time and again.
I don't find not wanting to clean BP unfortunate in the least. I love shooting BP, especially out of my lever rifles, and they're fairly simple to clean, not as easy as with smokeless, but not bad. Revolvers on the other hand are a pain. I have the utmost respect for those of you who shoot BP in your revolvers. You are patient men!
CHT