Every engine and transmission has its own unique mounting points designed in. Ford flatheads (with closed or 'torque tube' drivelines) for instance, generally use a 3-point mounting, with 2 mounts on either front corner of the block, and one at the rear of the transmission. The mounts are critical in an engine installation with a closed-style driveshaft (a single universal joint at the transmission, no rear universal, and no sliding splines), as much of the driving force to make the car go forward is transmitted through those mounts, as well as the weight of the engine. I mention this because many modelers completely fail to comprehend the relationship the type of driveshaft and suspension a car has to the rest of it. A flathead installed in an open-driveshaft application will still use the two front mounts (which will no longer transmit driving force) but not necessarily the same rear setup, which will depend partly on the transmission used.
Open driveshafts (2 or more universal joints, one at the trans and one at the diff, and a sliding spline arrangement to allow for varying length as the suspension moves) require the driving force of the car to be transmitted through the rear springs and whatever linkage controls rear axle movement, and the engine mounts in vehicles so equipped do nothing but support the engine's weight, prevent it from moving, and isolate its noise and vibration from the chassis.
But however the power is transmitted, each particular block design within a family will have cast-in bosses for bolts to attach engine mounts, and I always research the particular application to double-check where they are and what they usually look like. They're similar but different. What's necessary to convincingly mount an early Olds OHV V8 in front is quite different from the front mounts on a first-gen OHV Pontiac V8, for example.
Engine mounts in production or street driven vehicles usually incorporate some sort of rubber biscuit or doughnut (mmmm....biscuits) between the part of the mount bolted to the engine and the part attached to the chassis, for noise and vibration isolation. The chassis-side bits can be welded or bolted, the latter when several engine options were available in a particular body shell, or in those aftermarket installations where bolting is acceptable.
Racing cars of various types often dispense with noise abatement, and the mounts are often solid, sometimes in the original location on the block, and sometimes redesigned entirely, and becoming plates sandwiched (mmmm....sandwich) between the timing cover and the block, or the bellhousing and the block. In some cases, the rear engine mount sandwiched between the bellhousing and the rear face of the block is also the firewall of the vehicle, an integral part of the chassis.
Because of all of the variables in application and mount design, the best thing to do is to research each build individually if you're after technical correctness.
There is a sub-class of engine mounting, where the engine block itself is actually a stressed member of the chassis (see Ford Cosworth DFV F1 engine), primarily for weight and rigidity management. In some designs, longerons next to the engine carry part of the chassis loads, and in others the engine is the only frame the vehicle has between front and rear mounting plates. F1 cars have gone as far as eliminating any structure behind the front of the engine, using the gearbox as a chassis member too, and hanging the rear suspension directly from it. Needless to say, it takes some real wizardry in engineering to pull it off.
Edited by Ace-Garageguy, 06 November 2012 - 05:05 PM.