As someone that has built and still owns three M37s I can say that building an M37 that is capable of "half-way" keeping up with traffic is expensive.
I say this because if you plan on venturing out onto an interstate @44MPH you're going to be a danger to yourself and those around you. Even if you elect to go with 489 gearing you're only going to gain about 10 MPH and, with full canvas or even no canvas and little or no wind, the stock 6 cyl Chrysler flathead is going to have trouble pulling the 489s.
From a top end standpoint, the stock flathead will only deliver about 2500 rpm without jumping out of the frame rails which equals about 55MPH with 489s. If you try to spin the unballanced engine over 2,500 I suggest carrying around a whisk broom and a bushel basket to use for cleaning up the the cam, main and rod bearings that you'll be scattering around.
489's are great on level ground with a fresh engine but the minute you hit a grade you're going to wish you had a gear somewhere between 3rd and 4th. In other words --- the ratios are all wrong. M37s, great as they are, were built to keep up with the troops, NOT with traffic.
Last year I built a complete set of M37 front and rear axle assemblies, complete with 489s and front and rear lockers. The cores I used to build from were in good shape but still required a few bearings (seems like you always end up having to take a torch to one or two). Before all was said and done, I ended up with roughly $2,600.00 in the project.
This includes new high tensile rear axles, all new seals, new brake shoes and wheel cylinders, front hub spin outs and all the brass and felt for the fron knuckles.
I elected to stay with the stock drum brakes because I feel they are adequate if you keep them clean. IMHO where you have trouble with the stock brakes is when you do a lot of mudding and get gunk in them. Disc brakes are self clearning which makes them desireable if you like to get dirty. Going with an updated master cylinder might be desireable but I'm not sold on disc brakes on the grounds of inadequate brake surface area on the stock brakes.
The M37 that now has the 489s is a cut down "street rod" of sorts that I use to run around in. Even with the fresh motor, reduced weight and lack of troop seats and canvas (lack of wind resistance) I still catch myself wishing I had a close ratio 3rd gear.
I'll eventually build a install a modified Spitfire engine in this truck and the 489 power and top end problems will be over.
If I knew then, when I started playing with and building M37s, what I know now about M35s, I would have never looked twice at an M37. It's a lot cheaper (and rewarding) to make a M35 into a road worthy 4X4 than it is an M37.
In conclusion,To protect my investment and keep the resale value up, I'd build the M37 in stock military form, keeping the stock gearing and stay off the inerstate --- be safe and enjoy.
Respectuflly Submitted,
PS: A picture of "The Woogie" is submitted.