I will reiterate. Handle different guns and see what you like.
True, we can build whatever we want. It’s your business… but you did ask for opinions. A list of specs may look fine on paper, but in the real world the performance of such a gun may leave it wanting.
I build SMR’s from a blank; just two or three a year. Most of my guns carry a B weight swamped barrel, .50 caliber, and 44” long. That combination looks good, handles and balances well, and can be used for deer in every state (as far as I know).
I’m not an expert, but my research tells me that a .50 caliber was not common; but there were some. Barrels of 1” at the breech were somewhat common, with the vast majority being swamped. And at 44”, a barrel is really on the short end of average for an SMR. Locks were English.
When you get into barrels that are rifled for .54 or larger, you get into barrels widths that, in my opinion, will end up looking chubby in the breach area on a SMR. And if you change dimensions in the wrist, forearm, and butt to look good with the wider barrel… your gun won’t look like a nice slim SMR. Other styles of rifles are just better suited for the larger calibers.
I did make a nice looking SMR in .54 for my brother on a 44” C weight barrel. But his length of pull is 14 ½ inches; so I increased other proportions a little, used a Durs Egg lock because it’s a little larger than the Late Ketland I normally use, and it came out looking nice. But it’s a big gun… and my brother is 6’3”.
My point is… if you build a gun around the specs you have, the gun may not end up looking like the SMR’s you’ve been eyeing. It also may not end up handling like one either. If you use a straight barrel, and go for something 40” or longer, you will have a muzzle heavy gun… not a light well balanced one.
I’m assuming (which means there’s a good chance I’m wrong) that your success has also been with shooting the big bullets, and you may be uneasy with the thought of using a round ball on large game. I’ve never shot the bullets. But I can tell you, from personal experience, that a .490 ball pushed by 65 grains of 3f will go clean through a whitetail doe at 50 yards. Lengthwise. I also have a buddy that has taken three elk with round balls out of his old .50 caliber Dixie Mtn Rifle. I can also tell you that a .562 ball (.58 cal rifle) in front of 70 grains of 3f is an absolute thumper!
Handle nice longrifles with swamped barrels. Shoot them if possible. It will be fun research! There is magic in a long, slim, well balanced Longrifle. Unfortunately, you can’t achieve that magic by just throwing any list of parts together. A good Longrifle is the result of proper design, planning, and execution.
My two cents worth. My first gun from a blank did not have the proper design and planning. Execution was good, but the result is a rifle that I don’t use any longer… and one that I would not sell because of the design flaws.
Anyway. If you’re cutting live wood for the stock, then you have some time to think about things, and handle nice guns, while the wood goes through a proper curing.