292 has 7 main bearings. The 261 only has 4. The 261 would definetely be eazier to install with a manual transmission in a 1946. The brake and clutch pedals mount to the bellhousing on trucks till the AD body change. You would be kind of limited to transmissions with the stock bellhousing, but you could always have an adapter made to sit between the bellhousing and the transmission. An A833 (Dodge) overdrive transmission would work real well behind a 261.

I mention the dodge transmission because the input shaft on dodge transmissions is typically 1 inch longer than the input shaft on the gm transmissions, which gives you the ability to make a 1 inch thick adapter to have everything mesh correctly. You can usually hook up your stock mechanical speedo to the mopar speedo gear, and change the speedo gears to suit your axle ratio and tire size.

I will be putting a dodge NV4500 behind my 302 GMC inline 6 in my 1940 GMC. I will be able to use the stock clutch linkage, but the brakes will take some engineering.

John