Drive it like it is a few times to get a feel for the condition. Look for leaks before you clean it, then pressure wash it while it's still in running condition so you can run it after the wash and make sure nothing important got wet (like water in the cylinders and inside the TPS box, etc). Best to know it runs great before you pull it so that if it doesn't run great after the swap, you have something to go on.
Looks like a Jeep D30 front axle, probably from a early/mid 70's CJ. The t-case is a D20. Both are easy to get parts for. The front brakes may be a different story. If they have been converted to 6 lug, you will need to figure out how they did that and what parts they used.
There are a lot of aftermarket upgrades for both the axle and the t-case.
And it works well with open exhaust also if reasoning it to death. But in the real world works just fine with a smaller pipe and there's been no mention of a header or even if the engine is modified. At some point the law of diminishing returns set in.
Reasoning to death. That's exactly what you're doing.
I am saying that real experience shows that a 2.5" is not too large for an L4.
Don't keep throwing numbers out that confuse people. Let experience speak.
If 1 7/8 pipe will flow an L20B then a 2.5 pipe will flow 77% more air or a stock 3.5 liter.
I can't remember what the stock L20B pipe diameter is, may be 2" but there's no mention of cams, head work and induction. That said I doubt it will flow as much as a 3.5 liter engine. The cross section of a 1 7/8" pipe is 2.75 square inches. If you go to a 2.5" pipe the cross sectional area jumps to 4.9 square inches. Now that's an increase in area of 77% so if a 1/78 pipe works well enough for a 2 liter engine a 2.5" pipe will support a 3.55 liter engine.
Math doesn't change the fact that a stock blueprinted L16 with a DGV and a Nissan Motorsports header makes the most power (on a dyno) with a 2.5" exhaust.
Reasoning it to death won't change the truth. It just works with a larger pipe.
I use the L16 as an example, but the same can be applied to any L4. 2" is good, 2.25" is also good, and if you can handle the tad bit of extra noise, a 2.5" is the right choice for a spirited driver.
6-32, maybe? Don't quote me on that. If you have taps, just try to match the screw up to one.
Maybe, but it may also be metric. They were mixing and matching metric and SAE in that era.
Problem is that cable is threaded end where as stock is just a square end and set screw. Got to figure out a way to put stock knob on this cable. I think it came from a 510 but no way of knowing for sure.
You could fill the OEM knob with epoxy (JB Weld) and drill-n-tap it for the new cable.
Nice looking setup. I'm not a huge fan of the small miters. When I build exhaust systems, I like to keep the welds to a minimum, mainly for aesthetics, but I get it. They definitely serve a purpose. It's hard to wrap a downpipe around the torsion bar.
As far as the 2.5" goes, almost every Datsun L4 powered car I've ever owned had a 2.5" exhaust. Even the whimpy 125hp L16 we used in our ITC racers had 2.5". Some say it isn't necessary, but the dyno loves it on a L4. Most of my cars had the Nissan Motorsports headers with custom collectors so maybe that's a distinction worth mentioning.