I would recommend using the side engine mounts if your engine has the mount bosses. As Bill stated there would be too much distance between the standard front mount and the rear transmission mount. I have seen people make this mistake with
V-8 conversions by using the existing front mounts and a rear trans mount. It usually results in broken mounts and everything flopping around. In some cases the only thing containing the engine is the exhaust system. Danchuk makes a bracket kit (for cars)for those inclined to use the aforementioned set up. It mounts from the frame horns to the bell housing and apparently keeps stuff in place.
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