(per request)

On Loading an Antenna:

The SCR-274N and AN/ARC-5 radios were not designed
to load a 50 ohm antenna. They were intended for
antennas of about 5-12 ohms. In order to load
a 50-ohmer you'll need to do one of two things:

Cheap and easy- put a good quality NP0 (no thermal drift)
capacitor of at least 1000 volts between the antenna terminal
and the coax center conductor (in series).
For 40 meters, use 50 PF. For 80 meters, use 75 PF.
Non-NP0 caps may heat, drift and cause chirp.

More trouble but better:
Wind a 4:1 "UNUN," which is an unbalanced to unbalanced balun,
and use it at the antenna connector to match the coax.
The design is available in the Handbook.
Will cost a couple of watts but worth it.

I hope these tips will be of value to you.

Good Luck with it!

73 DE Dave Stinson AB5S