Fender made Roland-ready Strats for a few years. If you get one of those used, you’ll have to buy a GKC-AD 13-pin GK to Serial GK converter. This assumes you can live with its neck - 9.5" radius, modern C neck, typical Strat 25.5" scale. Just saying, because some people want flatter necks than that, or rounder, or wider, or narrower or…
https://www.sweetwater.com/store/detail/GKCAD--boss-gkc-ad-analog-digital-converter
I’d have to buy a GKC-AD to use a GM-800 with my Parker Nitefly, which has a GK3 (13-pin) pickup installed.
If I didn’t have the Parker, I’d shop for a sub-$1000 guitar to serve as a dedicated GM-800 guitar partner, buy a GK-5 pickup and install it on the guitar. For all I know double-sided tape to secure the pickup might be fine, which would eliminate the need to drill holes into the guitar. This way I could choose a guitar that feels good to my hands, rather than buying a guitar with factory installed GK pickup and hoping it will fit ok.
I understand the reluctance to put a GK-5 on a nicer instrument - hence the role of the cheaper guitar would be for. You’re more likely to accept sticky residue - or at worst drilled holes - on the on the cheaper guitar than on any of your costlier guitars.