I'm building a street 65 Mustang using a '99 Lightning engine and controls. Can I use the smaller 4R70 with the stock computer and harness? Will the converter bolt to the flywheel, etc.?

 

that wouldnt be adviseable to try unless you have a large supply of 4r70s behind your shed, ford hangs the 4r100 behind the lightning motor for a very simple reason..the 4r70 just cant survive that kind of punishment for very long, if at all, now being that you are going into a car that is roughly 1500lbs lighter than that rruck, this might extend its life somewhat, but if you are going to go to the EXTREME difficulty and expense of putting that motor in a 65 stang, why not do it right? by the way, have you done the ballpark measurements on this swap yet? a small block ford doenst leave alot of extra room under that hood, and very little between the fenders, and a 5.4 is roughly as wide as a 429. not trying to step on your dreams man, but it REALLY isnt a feasable swap.

 

Blue00,
It is feasible, I've done the measurements. I'm in the process of installing a Mustang II Front-end and removing the shock towers. Engine bay width is not a problem. Tunnel width for the tranny body is a different story. After my exchanges with Mark and other research, I'm down to two choices; 1) a compitition built 4r70 with the electronics removed will fit the tunnel but I will have a chip burned to disable the transmission computer controls; 2) enlarge the tunnel to accomidate the 4r100, make a custom front capet and/or modify the stock console to fit the new tunnel.
Cost of the 4r70 built to take about 550 HP and modified to operate without electronics (without a core) is about $1900.00 add $300.00 for a custom chip, so say $2100 will do it. A rebuilt 4r100 is approximatly $1900.00 (outright). Then I've still got cost associated with enlarging the tunnel and finshing the tunnel.
I haven't made the decision yet, but the modifed 4r70 looks like the easier solution if it will hold-up. The tranny builder says it will and provides a 12 month warranty to back it up. As soon as the front end is installed, I'm going to get empty cases for both trannies from a local shop, pair them with the engine and trial fit them. If it doesn't require too much hacking of the drive tunnel, I'll go with the 4r100.
FYI, I'm not a rookie, I owned and operated a performance auto center for 10 years and have personnel built and owned at least 5 street performance cars that include and engine swap. The last 2 were a LS1 powered S-10 and a 502 power S-10 Blazer (now there is a tight fit)

 

The 4R70W is a very stout transmission when properly built, don't discount it. They can hold up to 500/500 pretty easily. Check out www.reinhartautomotive.com for complete 4R70W trannys (I think you have to email them) or www.tccoa.com for doing the mods to the 4R70W yourself.

The stock 99+ mustang 4R70Ws are good to 400-500rwhp with a shiftkit....so says one of the ford driveline engineers.

 

4R70 will be plenty strong. Don't forget the Lightning weighs in about 5000lbs. Big factor in the tranny department. In a Mustang that is 1500-2000lbs lighter you should be fine.