I received the spike for the Deere 17/PL-4 and it was the right fit. Turns out there are a couple sizes and this one (64501) is a larger one. There would appear to be two smaller versions from what my searching turned up (combined with what's in the SL-4A IPL) with part number 65878 being a smaller one on ebay for the PL-9 and a 65299 "kit" listed in the SL-4 IPL which may well also just be the 65878 with hardware included. I didn't dig too far into it since I found what I needed, but suffice to say this seems to be one Remington part that doesn't have a Homelite match. I've included a PDF template for anyone who may want to make the 64501. (A couple hours with a plasma cutter could make someone some money knockin' a few of these out.)
Looks fairly formidable, though deceptively subtle at the same time. Should get the job done -- and this project now is finished. Thanks to Carl early on for his patience while I was trying to sort out the top end variants and options.