Hello all!
I used one of them several years ago, pulling a Nimrod (Jim Mannall design) and a Nobler.
VERY sweet engine, delightful break (one of the mildest I´ve heard).
Mine pulled a 10x6 at 8.500 rpm (just in the edge of 4-2 break) on the ground and was enough for a 38 oz model.
Fuel 25% castor 5% nitro.
My personal opinion, very good choice for any classic design.
Regards from Spain.