I will go against the grain a bit here. I very much like playing with persimmon and have played persimmon and blades about 90% of the time this summer, and score within a stroke of my handicap when doing so.
I will admit that it is less forgiving, at least with the driver, but as you increase the loft they become a little easier. Persimmon also requires a bit more care than metal heads, especially when it comes to moisture.
I grew up playing persimmon, so there is a nostalgia aspect for me. I am also old school in that I think only steel shafts should be used in persimmon, and the Dynamic or Dynamic Gold are about as good as you will do. That said, Louisville Golf and Joe Powell Golf both currently make persimmon clubs available with graphite shafts. Both companies take repair work, and would probably install any reasonable shaft in a persimmon club in good enough shape to handle it. Another source is Dave Wood, but I think he is more into restoration than reshafting, but could probably do it.
I do agree with everyone else though, that reshafting your MacGregors would not be economically feasible. You can purchase high quality brand new traditional persimmons with Dynamic Gold shafts from Louisville or Joe Powell for $175 to $225 per club. I think both will fit graphite shafts for a few dollars more. Louisville Golf makes some more modern designs in persimmon with graphite; I have not personally played those.Very nice used clubs can be found on Ebay and Craigslist for $25-$75, and often in pawn shops or antique stores. In my vintage bag now are 2 Joe Powells and a MacGregor so aquired, and in which I have a total investment of $45 including $24 of new grips.
If you look at my sig you will see I am not opposed to titanium and graphite and I have a fondness for my Callaway hybrids. I can easily hit my Callaway 3H the same distance as my Wilson Staff forged blade 1 iron with less fuss. You can buy the almost latest (3-4 year old) driver or fairway in great condition with a great shaft for probably less than it would cost to reshaft your old MacGregors.
There are days, though, when I just enjoy a simpler time knocking a ball around with the old lumber. I don't know if I will ever swear off new tech completely, but I am playing vintage more and more.