Unless you happen to find a split boot that will fit the axle (I'm not going to comment on the use of them since I was going to try that route myself.) you will have to tear the axle apart to put a factory boot on it.

Homokenetic vs Annular

Annular is all 1 piece.
Homokenetic the differential side is bolted to the shaft.

I'd load a picture of it but I've already loaded the picture elsewhere on the forum and the software won't allow me to load it again.

Carquest has the axles for a 300D for like $200 with a $120 core charge. My wifes 300D now has 1 homokenetic and 1 annular axle from them.

I will note that personally I prefer the annular axle. I've put 2 homokenetics on my wifes car. Within 2 months the first axle came apart. Aparently the bolts were loose and they worked themselves out. Fortunately I was leaving a stop light when it failed and therefore didn't cause any damage to the rest of the car. Regardless, I check the bolts on the 'new' axle every week or so.

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'84 300CD Turbo 132k (Anthracite Grey) - WVO - My daily driver - Recently named coo-coo-coupe by my daughter.
'84 300D Turbo 240k (Anthracite Grey) - Garage Queen
'83 300D Turbo 220k (Orient Red) - WVO - Wifes daily driver

I'm not a certified mechanic, but I did stay at a HolidayInn Express last night.