Hello & welcome to the forum.
I take it your having the head done, skimmed & a rebuild of your own engine & not buying a new one.
you will find some stuff in here in 'V8 wizard' & FAQ's
www.v8engines.comThey may even have a sound second hand engine that left from them doing a transplant/conversion.
You could speak to Jim King @ Lethenty Mill,
This is a garage which is between Daviot & Inverurie.
www.jimkingautotune.co.uk/contact.htmlHe is a member of the 'Buchan Off Road Drivers Club'
As already said its Worth looking on their website,
& possibly posting as there are some other garages in the area used by club members.
Or Mann Automotive in Laurencekirk.
a bit far possibly depending where you are but they know their stuff.
Dunecht Garage doesnt do there own big work but can possibly point you in the correct direction
of who they use.
One place in Forfar, but he will not touch a P38.
all the best.
george