His call sign did start with a K, so amateur extra will be what I have to shoot for.
But, what was the format of the callsign? Amateur radio callsigns can be 2x3, 1x3, 2x2, 1x2, or 2x1. Was it two letters, then a number, then two more letters? For example, KO6JW above is a 2x2 callsign and he got it while he held an Advanced license.
When you get your Technician license, you will be issued a callsign from the sequential system. Technicians are eligible for a Group C (1x3) or Group D (2x3) callsign. The FCC will issue you the next available callsign in the sequential system. Since you live in Missouri, the number in your FCC-issued callsign will be a 0 (zero). In "zero-land", as well call it (CO, IA, KS, MN, MO, ND, NE, and SD), the Group C callsigns have all been issued using the sequential system, so you'll get the next-available Group D callsign (most recent one issued was KF0FXZ).
As a Technician, you'll be able to apply for any
available Group C or Group D callsign as a vanity callsign.
When you upgrade to General, you can keep the callsign you got as a Technician or you can request an automatic callsign change through the sequential system. But, Generals also get Group C or Group D callsigns, so you might as well keep your Technician callsign. As a General, you'll be able to apply for any available Group C or Group D callsign as a vanity callsign.
When you upgrade to Extra, you can keep the callsign you got as a Technician or General or you can request an automatic callsign change through the sequential system. Extras are eligible for any Group A, Group B, Group C, or Group D callsign. As a General, you'll be able to apply for any available Group A, Group B, Group C, or Group D callsign as a vanity callsign.
The rules for requesting a vanity callsign as a close relative of a deceased former member can be found here:
Request Types: By Close Relative Of Former Holder Now Deceased