Step 5: Chassis
The foundation of your project, chassis building is a very important stage of your project. Remember every modification will require engineers certification for registration. So you need to plan and design what you intend to do. If you don't follow anything else out of all of this there is one golden rule. Get your chassis/suspension finished first, then start work on the body.
Most original chassis are by their very nature severely lacking in the structural requirements for a modern hot rod. They are typically 50 to 70 years old and have been subjected to the ravages of nature, pitted and rusted. Most will require considerable repairs and reinforcement in the form of boxing to withstand the forces of modern V8 motors. Plus with the changes to front and rear suspension systems and power trains, there will be numerous bracket and holes to be removed, replaced or filled. Given all these changes it is common practice to replace front, rear and internal cross members. So at the end of the day you actually end up with very little of the original chassis left.
If you are using a fiberglass body, using an original chassis has one distinct advantage in that your hot rod will be registered as a vehicle of the year of chassis manufacture. ie 1934 and will only have to comply to ADR's for items that have been modified.
There are now a number of manufacturers of replacement or new chassis rails. The construction of these varies considerably as does their similarity to the original product and this will all effect their suitability for your project. Some manufacturers have gone to the trouble and expense of pressing the rails, this is the same manufacturing technique as the originals and say for '32 rails give the opportunity to include the reveal in the side of the rail. This produces a "C" section. Other manufacturers will build their rails out of 2 individual pieces of plate steel, cut to shape and then welded into the familiar "C" section. Or with a fourth section completely boxed.
I'm not about to say here that one is better than the other, rather I have drawn your attention to the different techniques.
If you are using a fiberglass body ensure with your engineeer or registration authority that you can use replacement rails. If they say no, your hot rod will have to comply to all current ADR's and be registered as a current year vehicle.
Some body styles will take a chassis swap very well. For example there are now a couple of Australian body makers offering Toyota Hi-lux chassis with the correct mounting points. Pick ups like the F100 often ride on a Holden 1 tonner chassis.
The hot rod chassis obtains most of is strength and rigidity from the center crossmember. As well they usually provide a rear mounting point for the transmission. Early hot rod cross members were constructed of similar section to the original chassis. However the modern configuration uses square or circular tubular sections in a cage design which allow for exhausts and other lines to run through them allowing the rods to sit lower than before.
Motor and Transmission Mounts
This usually has a lot to do with what chassis will be used, as most authorities base the cars origin on the chassis. So if you were to replace the chassis with a new one or do a swap, the rod would then have to comply with all Australian Design Rules from the year of manufacture of that chassis.