Tony,
Sorry, I have found an irrefutable, infallible, indisputable document !
"Notes of a meeting held at offices of Watergate Shipping Company, Newcastle upon Tyne 06.10.1970:"
Subject: "To decide on action to be taken to alleviate the surging which occurs on the forward turbo charger at speeds exceeding 92 - 98 r.p.m."
Present: Mr Peter Dalgliesh, Mr.R.N Dalgliesh; Capt. R.G.Phillips; Mr T Middlemiss; Mr. C.W Matthews (all Dalgliesh staff). Mr P. Pfeifer (Brown Boveri). Mr. A.J. Wickens, Mr B. Gray (Hawthorn Leslie).
Other documents including one from Doxfords to Dalgliesh all have quite clearly a 670PT4 engine.
I have no idea as to why a P type engine should be built in 1968, other than the contract must have been signed before the J type was proven. The first one was North Sands and that wasS 1965. Maybe Hawthorn had enough P type bits lying around to build a whole engine and thought "Why Not?" then offered Dalgliesh a good deal for accepting a then obsolete design
Tom
ANOTHER EDIT:
Tony
I've just spoken to the last Chief draughtsman at Doxford engine works and he instantly recalled that the engine was a P type that had several J type components added to it. You will know that Hawthorn Leslie were prolific engine builders in their own right but also built numerous Doxford engines and collaboration between them and Doxfords led to the unsuccessful Seahorse engine. That apart, Doxford licensees had a certain amount of liberty to change the design of components, and frequently did, not all of which were received enthusiastically by Doxfords, (and vice versa, no doubt). He told me that Hawthorn built two P type engines with various J type parts added to them and that Tamworth was one of them, and that a similar thing happened when the P type replaced the LBD design. Tony Wickens, who was a long serving Hawthorn engineer and would even know the names of all the mice in Hawthorns works :, and who would be able to give precise details of the engines, is still recovering from major surgery and will have more things to be concerned about than this, otherwise I would have asked him what the additions were.
The all defining criteria would be the crankshaft. The P & J type crankshafts were radically different and entirely non interchangeable so you may have a P or a J but not both and the Tamworth was a P.
An intersesting one. I wonder if I might ask how you came to find it as a J engine?
Tom