What's a pack mule?

If it's a loaded tourer destined to do hundreds and thousands of kms with gear, I'd rethink the plan. Get a light, strong purpose made frame to start so you won't need to break the bank to add braze ons for all the accoutrements you'll need.

If it's a townie beer/grocery/trailer hauler then spend whatever you want but it should be done cheaply - again the frame really doesn't merit the investment. Wheels? Yes, definitely. Gotta pic of said Higgins mule?

This is all worth 2 cents.