Thanks Blackburn, I was beginning to think a plate with suitable holes drilled in it might fit the bill and then decided to buy the one left at ex-MOD as suggested by Wireman. I was pleasantly surprised to discover I still had a credit on Paypal which covered half the cost. I'll probably put the tool on ebay when I'm done with it as, I hope, I won't be delving so deeply into the engine again once it has been rebuilt and if I get a reasonable portion of my outlay back it will probably be a fair compromise, taking the time/cost equation into account, as I don't have a handy lump of steel of adequate size to hand to knock up a suitable tool.