Hi Gig10,
Only a few of the 1948 Pacemakers had the Schwinn springer and only a few had the "H" motor. I suspect the handfull were really proto-types. The production 1948 Pacemaker and all later versions had the Whizzer front suspension. All were 24" and all were maroon [the 1948 was darker than the later Pacemakers], and the 1949 and up were called Whizzer red but were maroon. The Whizzer front fork is different on the 1948 model in 2 ways, first it used a different rubber cushioning system than later models, and secondly it doesn't have the "safety circle" on the lower fork tubes to connect 3 fender braces.
The serial number on the very early pacemakers is located at the bottom of the front down tube near the pedal crank housing. The later Pacemakers has the number stamped on the front side of the pedal crank housing.
The fuel shut off valve looks like the correct version for the Carter, only the Tillotson carburetors had the glass bowl with shut off.
The Carter carburetor for your bike should be a fixed main jet and have the numbers 665s stamped on the right side of the mounting flange. I will attach photo of correct carburetor [on the right] and you can see the removable brass fitting.
Only the 1948 had the clamp-on style motor mounts all future models had the bottom & top rear mounts welded to the frame.
The early 1948 is the most rare of Pacemakers and the majority ran at 37 MPH with the "J" motor. My 1950 [stock] will almost reach 45 MPH.
The 1948 Pacemaker was released June 1948 and Schwinn made all the frames except for the first 1000.
All 1948 Pacemakers had rear coaster brake [New Departure] and most had the SA front brake.
Your bike has most of the original parts and will be hard to find one any closer to original.
I use the electronic ignition module in all my personal Whizzers and I doubt it has a rev limiter. It was designed to replace the ignition on most lawn mower motors, therefore I wouldn't see the need to limit the RPMs because most [99%] have governors built in.
I have never had any of my vintage motors above 5500 RPMs, some of my friends have motors turning above 6000 RPMs, so I can say it isn't limited to under 6000 RPMs if at all.
Have fun,