Hello Fairlane71,
your question was posted more than a year ago, so I hope you're set to receive email notifications on your post.
I have a small amount of knowledge about 2v heads. From what I can make out, they respond
very well to turbo charging, especially with some head work. The 7-main bottom ends are virtually bullet proof, so turn it up to the max (after a suitable rebuild of course).
If you wish to retain matching numbers, stick with the 221 of course, but if that's not an issue, I suggest you find a 250 motor and slap the 2v on it. There is an issue with the gaping hole that is 3 & 4 exhaust port, but there are port dividers available in the states, not sure about here in Oz.
If you're really serious about performance, there is an aluminium 2v head available, based on the Aussie 2v. It was designed and developed in the U.S.A. (Have a look here and take the time to read up on the development
Classic Inlines Performance Parts - Home), but is cast in Melbourne by C.H.I. Call John (03)9583-5725.
All the bolt-on stuff (rocker covers, rockers, inlet and exhaust etc.) is completely interchangeable with a stock 2v, and 3 & 4 have separate exhaust ports.
They're claiming a potential 500 hp with forced induction, i.e. turbo and/or supercharging.
NO, I don't work for them, I'm just hooked on the 250 motor, the forgotten powerhouse.
Bear in mind the yanks built thousands of mustangs with sixes, none of which we ever saw here, hence their interest in extracting horsepower from this mighty motor.
And
please, stick with your 6, you won't be disappointed in the long run. If anyone tries to tell you to drop a v8 in the old girl, smile and say nothing, they just don't get it.