You really are enjoying yourself Polybus! lols.

You will see and here of all sorts of crazy mods as you go along and learn more,but your head example is one ive not heard of...haha.

Youll find most parts for these models are still fairly common and cheap with the exception of the choke assy and Special badge. Fuel taps and snorkels are actually getting more scarce also,but not too pricey.
So dont worry to much if you break anything. Probably the rarest part on your mowers is the mesh guard on starter of the M5 S3,so keep it safe:) Anything else is pretty much still easily obtainable smile

Good to see your getting right into them!