Be sure to use the updated, single output tube version of the schematic and layout, the original 2 output tube version from the book will only work with 2 6V6, although you could build the original 2 output tube version and use just one 6L6 (or other output tube) without over-taxing the transformer. Read DH’s addendum as it addresses some vague layout issues in the book.
Andy’s impedance comments apply to the output transformer secondary’s (speaker load).
Merlin Blencowe’s books are the best. If you read those, 2stroke mods are sure to follow
Good luck, it’s a neat design