well, I'll chime in.
I humbly suggest:
First. you have to realize how much you are willing to spend vs. your desire to preserve what you now possess.
http://www.earlycj5.com/ is full of discussions on mild mods and tricks that would test your abilities, wallet, and patience, so be prepared!!!
your immediate issue is taking a 50 year old vehicle at current Interstate hwy speed limits that would not only test your manhood when evading an catastrophe but would conflict the originally intended, mechanical design of :
Pitman arm actuated steering
9" drum brakes
The f134's long rods that are not likened to excessive rpm's (over 3000 for extended periods of time and basically a tractor motor)
24 Volt system that usually cant be jumped by your AAA gold membership card
Not to dissuade you from your potential bliss, I would concur with the others and these tips to offer from experience with my Mjeep:
-Seat belts!!!!!
-Switch out the rear STOP and Black-out lights and get the lenses for a
Gamma Goat brake lights....
-Get a Turn signal wiring kit for 24volt ...typically found for M151 and M715's
-Selectable Locking Hubs-(FRONT)
-self explanatory
-Warn Overdrive hands down.
-keeps the revs low on highway and incredibly versatile when on the trails.
-Get a rebuilt or New from Hermtheoverdriveguy.com Period!! he stands behind
his work. You may find one for 350-600 $ on the net or ebay as used.
It may cost you another 500$ just to rebuild and ship, etc,etc
Not worth the risk and headache to buy used take off
-11" drum front Drum Brake swap - great improvement!!
check out the earlycj5.com for info. (lots of info)
-Single piece tie-rod conversion - simplifies the linkage steering behavior and
reduces if not eliminates steering back lash.
-LUBE < LUBE< LUBE!!
the above got me 60 mph on the flats at appx 2800.rpm well tuned young motor and drive train on 235/85-16 radials. (no lift kit or suspension manip) and some peace of mind at that speed.
I got to 71mph going downhill 15 deg grade by dropping the W/S w/ a healthy tailwind
other mild bolt on considerations applied that ADD$$$$ time, skill, and patience:
Swap Carb > Weber 32 / 36 progressive carb (you'll need an electric fuel pump that runs on 24VDC or a regulator on your existing.
Machine Deck (mill) your head .060"
Re-curve cam
Synthetic Oil (Motor only)
Port /Polish match exhaust
Swap exhaust to 2" or 2-1/4"
K/N filter conversion
The above may or not provide your desired results.
All doable/reversible with minimal visual alteration.
hope this helps.
Personally, I'd leave her alone, M38A1's complete in a state such as yours are rare finds. though its your ride on your dime. have fun!!!!