There are several head types but on a 2.5 you have either have one piece heads that uses a gasket or a flat head that uses O-rings and powerheads are
I would not spend any time trying to adapt a system for this.
There are lots of old stringer drive parts are out there.
Find what you need,
Just ordered the factory service manual (eBay for $28 - not bad) - I'll keep you posted!
Boobie- Thanks so much for the response. I greatly appreciate the knowledge you and others so willingly share on thsi forum.