Jim, the OS factory conversion parts are available from Tower.
You need—
The FP 40 venturi, OS Part No 23312000, Tower Stock No LXCX05, $11.99
OS 20-25FP-S NVA, OS Part No 22311000, Towqer stock No LXCR49, $13.49
I suggest that you also order the FP 20/25 Venturi, OS Part No 22312000, Tower Stock No LXCW99, $9.49.
The FP 20/25 venturi is worth a try but probably too small. However, we have several successful LA 46 installations at our club that used the small—and no longer available—FP 35/40 venturi. Bore the FP 20/25 venturi to 17/64" dia and you have an equivalent to the small FP 35/40 venturi.
All this stuff bolts straight into the front of the crankcase without any drilling of crankcase or venturis—easy!