Unless the track owner is your Father-in-law, be prepared NOT to be able to run the car down the track in stated condition.
A consideration for the IN & OUT box is determined buy some factors
How far the motor is out from the rear end and is there one that will fit without changing that dimention
How many push starts and stationary idles you plan on doing that you for the most part just slide the couplers apart (zero cost) in the pits or at a show. If you dont get real stupid with the clutch assy, holding it in for a few minutes during a Cackle parade/push start Cackle should not present a problem. If its your desire to have one, then go for it. I think the one by the Hampsire Bros will fit a close coupled design (motor out 26")
If you desire is the look and not a restoration of an original documented car, then go with a Chrys 8 3/4 rear end. Physicly the same size as the '49 Olds and if you were to swap the rear covers, you could not really tell the difference and the parts avail is 100 to 1 and is a period piece because they were available back then. Any Olds parts you see advertised know are for the later "Big" Olds and will not be correct for your build. Low gear ratios came in ambulances and milk trucks and all but gone unless somebody is hoarding them.
Chassis componants are not that difficult to obtain, I can build a period correct front axle with original Anglia spindles and can even do a front torsion assy, But why even stop there and have Me or someone else build the basic car for you and you can finnish it.
Starting a project like this without a basic understanding of the parts involved and getting input from all directions thrown at you will prove to be difficult - costly - time consuming. If its because you cant afford a pro- build? but you can afford the mistakes?
Pick a single builder that will work with you to build what YOU want and start there
