If you're not planning on doing anything fancy with it, you could take your head to most any good engine machine shop and you should get a decent result. However, I would tend to prefer in order of preference:
- shop that has experience preparing performance mods for your engine (twin cam or renault?)
- probably experience with with preparing foreign racing engines in general
- a shop with experience with your engine
- a shop with experience with foreign engines
- a shop with experience preparing performance engines of any kind
I tend to favor performance shops because if they are good, I think they are a little more exact and a little more careful. If they have experience with your engine, they may know a trick (good parts supplier, a good modification, something to watch out for, etc.). You don't list where you live, but unless you're far away from a decent size city, you probably shouldn't have any trouble finding a local shop who can do the job. You might ask someone in a local car club if he knows a good shop (a lot easier now with the web!). If you really are in the boonies, you could try calling Dave Bean (on the phone, his catalog and website hasn't been updated in quite a while) and asking him for his advice - and then take it. In fact, you could do worse than starting there. Dave probably knows as much or more about Lotus engines than anybody (when he had a shop, he built a beautiful engine for me).
Good luck!