You have a couple if choices as I see it. I have a 46 coupe, BTW.
First is a frame swap, but with a custom made chassis from one of the major suppliers like Heidts, Fatman or TCI. This gets you everything you need, chassis wise in one purchase. It will have the updated suspension, with options and should be a bolt in swap. Bolt in is somewhat of a joke in the hot rodding world since very little is truly bolt in, but the custom frame from a reputable supplier should put you miles ahead. They will be able to incorporate mounts for whatever engine/trans package you want, within bounds of reason. Some engines, like say a Coyote Ford MAY require major body mods to fit.
I am not a fan of late model frame swaps. While they offer a cheap modern chassis, they require extensive mods to the floor of the car to make work, usually. Here you would have to realistically rate your ability to make these mods in a safe, workmanlike manner. The mid-60's GM cars like the Chevelle have been known to work out wheelbase and width wise.
Second choice is to modify the chassis already under the car. The 41-48 Fords had a decent chassis that is strong enough for a cruiser. Mine has held up to a 383 stroker with no issues. It currently has a 350, but I plan on going back to the 383 soon.
The 46 chassis has an X-member for torsional strength and that should not be removed unless you can add the strength back in some other manner. The X does limit transmission fitment severely. Something the size of a TH350 will fit with minor trimming but larger overdrive transmissions will require major surgery to go in. A standard SHOULD go in ok too. My future plans may include a 5 speed manual in place of the auto it has now.
Not sure if they are still in business, but Chassis Engineering used to sell bolt in suspension upgrades like parallel leafs in the rear and I believe they even sold a bolt in Mustang II front kit. The stock front suspension is not terrible if its in good shape. The 46 was at the end of the straight axle Ford production and they had worked out most of the issues. In some builds, depending on transmission, you can simply lower the A-frame (wishbone) mount lower on the chassis and retain it. This allows the front end to work as Ford intended. Just rebuild the stock stuff, add disc brakes and update the steering box edit: and add tubular shocks to rreplace the stock lever shocks. Several folks used to sell adapters to add a small Saginaw power steering box in place of the stock Ford box. Adapting the steering column would be up to you, but should be fairly simple with all the aftermarket steering components available now.
You could order a complete 9" Ford rearend width brakes in whatever width you need from several suppliers.
Late model master cylinders can be adapted to the existing pedal and stay under the car. Power brakes can be adapted as well.
Engine choice is a personal thing. The reason that a lot of these old cars wound up with Chevy engines actually has to do with Ford's decision to move the distributor to the front of their later model engines. This required the oil sump to be in the front too and that interferes with stock Ford front cross member, requiring a bunch of major fab work to fix. Also, Ford engines tended to be longer than Chevys. These issues can be worked around by swapping oil pans (Bronco) and replacing the water pump with something shorter. A kid working with home tools in the 50's could by a set of motor mounts and a bellhousing adapter and stick a 265 or 283 Chevy in an old Ford in a few weekends. Not so much with the Ford v8's. Most people back then didn't have access to the fab tools we take for granted nowadays. That trend continued for many years after parts became available to swap the Fords into a Ford much easier. The Chevy in an old Ford is still easier, IMO, but the Windsor Fords go in pretty easy now, too. Can't help at all with the Ford transmissions.
Price? The flip answer is whatever you want to spend, but in reality, figure no less than $30 to 40$K (most likely more) if you do all the work yourself. High five figures to low six figures (and 1 to 3 years depending on their backlog) if you have it done by a pro. Paint and body alone could easily eat up $10K or more. As was said, if that is what your friend wants, it makes much more sense both time and money wise to sell the current car and buy a completed street rod that may only need a few tweaks to be the car he wants.
