JP
I'm in the midst of a major modification of my P-15. I drove the car for many years with the flat head. It is, and can be, a really pretty engine. It's a great looking car too. However, the flat 6 will never be fast,.....or even "sporty" to drive.
If you are of a mind to "modify", there are a myriad of things, simple to complex, to do. (Please don't put a Chevy in it.) Also, if this is a first time project, I strongly suggest that you start with some small items that will not disable the car for any length of time. Jumping in and disassembling the car or a major sub-assemby has the potential of turning into a multi-generational project. It's a shame when your kids are trying to figure what to do with that particially finished "dream" of Dad's.
Check my thread "I'm back" on this forum. I've obviously got a big project going. If you would like to know more or see it in the flesh, I love having visitors