I have that potbelly for 102's. My ferrules hold my various whips. Just want a light duty spring for ferrule to sit on.Just for reference, here's a Hustler pot belly spring. This us what I thought you were using.
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These are best for 102 whips but they are heavy.
Seems like your on track to adapt your Larsen whip to suit your needs.
My Little Tarheel HP only came with a 32 in whip that's really flimsy that I thought was cheap.
You could use that 32 in whip holder for the longer Larsen whip but you may need to drill out the whip holder some if the Larsen is thicker.