I would suggest that you post a picture of the adapter plate and that may generate some
suggestions. A 261 would have a 2 bolt starter that bolted to the bellhousing. V8 starters
also bolted to the bellhousing with 3 bolts in that era. Later engines with automatic
transmissions usually mounted to the engine.
Fred


1956 3100 Pickup/Red/350/3sp OD/PS/Disc Brakes
1957 Bel Air Sport Coupe/Red/355/TH350/PS/Disc Brakes
2017 Silverado LT Single Cab SB/Black/5.3/6 Speed Trans
1947 Willys CJ2A w/F-Head engine