I wouldn't want to heat my rods to 300°f, just take them to a good engine shop, plenty in the UK still
Neither would I. Read the message again. Put the PISTONS in the oven. Gudgeon pins in the freezer. The rod small end bushings should be a smooth, non-resistance fit at room temperature. It won't hurt the pistons. It won't hurt the gudgeon pins. And the rods are at room temperature.
The chance that an engine shop will know how to deal with, or have the tools to work on, the R16 engine are slimmer than they were decades ago (non-existent in the US, and one shop in canada IIRC), from my research. May be hit or miss. But, that is an option.