I doubt there is anyone here that answer your question:
Which radio set was the most commonly used in the M38?
Different needs of individual units, different needs of different military branches, different needs of Active vs Guard/Reserve units. coupled with the odds of someone being very familiar with all of those installations, in all those services, active /reserve/guard makes that one person impossible to find.
Also the M38's active military life was largely a very short span of time. The Army was very quick to standardize the comm jeep on the M38A1 chassis as soon as the A1 came on line because of it's greater Hp and weight carrying ability.
Your best yardstick for what would have been most common is what is still readily available from the surplus market's down the stream parts availability.
Use a simple checklist for your decision process. For example:
1 - Which service do you want your jeep to represent?
2 - Which unit or branch of that service do you want your jeep represent?
3 - What is the primary mission of your selected unit?
4 - For the Army, you will have to determine which of the Big 3 Frequency ranges your unit will be using. The spectrum was divided between Armor, Artillery and Infantry.
is there any one supplying these parts in good to very good condition?
There are several suppliers. Try to stay with suppliers who are primarily comm equipment suppliers.
http://armyradio.com/arsc/customer/prod ... age=7&js=n
There are many informative military radio web sites:
http://www.nf6x.net/1999/01/1950s-vehicular-radio-sets/
Mark's Green Radios Page is a good one.
http://www.nf6x.net/wp/wp-content/uploa ... nstall.pdf
This is Mark's PDF set of M38/M38A1 radio installations published by the Army Signal Corp.
https://www.qsl.net/pe1ngz/army/army-us/us-comm.html
http://www.grc9.nl/grc9uk.html
Even Dutch and other countries sites.
For static display radios, and light radio sets your stock 25 amp is fine.
I would avoid the 100 amp system the Army used back then. It was expensive, difficult to maintain and still hard to find parts for.
The Army's 60 amp alternator is the best all around beef up for your original 25 amp jeep. It is a one wire Alternator with built in voltage regulator. A wee bit expensive going in but very reliable and more than adequate for the radios.