You can get stroker kit's that will bring up the displacement to 500+ ci for big blocks. Now that would be a fun motor! The only thing i don't like about the big blocks is the oiling system. The cams have two holes drilled into them and when it turns it will feed oil to one head at a time not constant. That's why you see people run external oil lines from the oil pressure port in the back of the motor. These are indy heads but you get the idea.

 

I'm thinking we sure are free with the OP's money.

 

Kinda like the government.

 

The other handy thing with a Magnum is to get it with an OD trans.

This is more of a struggle with a 383-440 as it means more adapters, and separate donors.

 

Years ago, a fellow I worked with bought my '77 New Yorker Brougham. The 400 was bored and rebuilt with major inner modifications and was around 406 inches. It was the car I nearly lost my license in. (124 in a 55.) He's offered to sell it back for what he paid for it years ago. I'm sure the engine needs a slight refresh but it only had 25,000 miles on it and the transmission was still shifting good. The rear end was going out and I parked it. Tin worms were starting on it at the time too.