Jowett Jupiter 1951 with E46 drivetrain

[Carl Ring]

Hi folks,
I have an old sportscar, a Jowett Jupiter which has a strong tubular frame and aluminium body. Curb weight is 860 kgs. The BMW engine that goes in is M54B30 with 231 hp. The original engine had 63 hp, although the car won Le Mans three years i a row, Monte Carlo, RAC and other races. Only a year ago it won Le Mans Classic again.
So, now with the new power plant it should beat the shit out of most cars. The road holding was this cars strength with torsion suspension all around. The former engine was positioned forward of the front axle! Now the B30 will sit behind it. You will shiver and tremble when you see this coming- if you reach time to observe...
Now, head into questioning:
The Jupiter has a body width outside the wings of 1570mm. Inside and clearance the track forward/aft can be 1559 mm maximum.
The car is light and will have a track of 1490 in front and larger 1490 aft. Why is that on E46?
What do I do to get the wheels inside 1550mm? Or do I have to make a beating on this jewel to make it wider on the body?
Understand that I will take the whole drive train from E46.
With standard rim (8" and 225 tires ?) it needs 1593 front and 1653 rear if I go for 195 front and 245 rear., meaning widening 43 body front and 46 rear, an action I would not find handsome. This based on E46 original ET 41.
Now, how would a higher ET rear and 225s change the handling of this car?
Other than this-
What if I have wide rear tires on this light car? Will it run steady as a glue stick on the road?

I would enjoy to hear your expertise on this. Thankyou. By the way, I don´t know how to insert pictures, so google pictures of the racing version.

[Jim@tirerack]

This is way above my pay grade. I will say that wider and better traction/handling tires should make it handle much better. The balance front to rear I can not comment on.