The Toyota four-cylinder 8-inch rear axle is a drop-out style which makes it more easily serviceable. Most Toyotas used 4.10 ratio ring-and-pinion, which is sufficient for powering up to 32-inch tires.
Solid-Axle Swap (SAS)
The A-arms and the torsion bars used in the IFS setup are strong and can provide very decent performance in many off-road driving situations, but travel is limited compared to most solid-axle leaf-spring setups. Concerning strength, the biggest issue arises when the IFS axle halfshafts are forced to operate at steeper angles due to larger-than-stock tires. The shafts often break in such situations.
Since Toyota still produced a solid front axle version of the pickup for foreign markets, this meant that the front frame area on IFS rigs was still strong enough and the right width from the factory to support this setup. It didn't take aftermarket manufacturers long to figure this out, and solid-axle swap kits to replace the IFS and torsion bar configuration soon became available.
The stuff you'll need to complete an SAS is available as a complete kit from a lot of vendors, but you could make your own using used and custom parts. Many vendors offer the pieces separately for those who want to construct an SAS on their own. Most off-the-shelf kits include a front spring hanger kit, spring perches, shackles, and springs. Other items that are often included in SAS kits are front shock hoops to facilitate use of longer travel shocks. This is also a good time to locate a high-pinion frontend, but a regular four-cylinder 8-inch frontend will also do the trick. An IFS steering gear is already in place, but you'll still need some high-steer arms, a pitman arm, and a drag link and tie rod to complete the steering system. A new front driveshaft will also be necessary.
The Toyota 8-inch rear axle in IFS trucks is 3 inches wider and uses larger 11.5-inch rear drum brakes. Earlier models used 10-inch drums. The greater width permits use of larger tires without hitting the frame rails.
Suspension
All of the Toyotas in range can accommodate up to 32-inch tires in stock form, however, the '79-'85 Toyotas can get extra clearance for a 32-inch tire using extended shackles and/or rear lift blocks. Two inches of lift can be achieved in this manner and it typically won't require new springs, shocks, or brake lines. However, a slightly taller shock will lend further ride improvements and extend wheel travel. Installing more than 3- to 4-inch lift springs will require extended brake lines and suspension and steering-correction items like an adjustable drag link, sway-bar extensions, and torque-rod drop brackets. Lifting the rear of the vehicle can be completed using lift blocks, add-a-leaves, or new lifted leaf-spring packs. Body lifts are also available for all of the Toyota truck and 4Runner models in range.
The '79-'85 trucks and 4Runners used a suspension torque rod up front to control axle wind up during braking and acceleration. The rod gets too short as a vehicle is lifted and brackets are available to adjust it to the appropriate height or adjustable rods are also available to lengthen it as needed. An adjustable drag link is also helpful in maintaining factory steering effects. You can run without the torque rod in place, but you will likely experience pull to the right under braking. This is due to the axlehousing rotating which compresses the suspension and moves the drag link. This effect will be lessened in trucks with IFS steering gears and crossover steering arrangements.
In 1986, Toyota changed the front suspension configuration of its trucks and 4Runners to use an IFS setup. The IFS used upper and lower A-arms paired with torsion bars and shocks. The rear suspension on IFS trucks and 4Runners retained the leaf-spring arrangement. In 1990, the 4Runner was redesigned to use a rear coil spring four-link suspension and front coil spring strut arrangement. Rear coil spacers and front ball joint spacers can create lift in these models. You can also replace the rear coils and control arms for more lift. All of the IFS model Toyotas can be converted to use a solid front axle and leaf-spring suspension, which will offer the greatest improvements in vehicle capability and permit use of the tallest tire sizes.