I bought a kit which included parts for the linkage from Richard (now called Lotus Supplies at
https://www.lotus-supplies.com) so I can't advise you about some of the details other than refer you to this page (
http://www.greytower.com/jon/lotus/europa/gearbox/gearbox.html). I didn't have any welding done on my bell housing and didn't know it was advised till I saw that page. So far so good but at some point, I might have it done.
I don't think you'll necessarily need the output shaft oil seals. I wouldn't bother with the bell housing gasket either. For that as well as the end cover gasket (which I believe is NLA), I'd use Permatex Right Stuff.
I'm not sure about the speedo drive oil seal but if you plan on using the stock speedo and cable, you'll need another speedo gear. I'd recommend an electronic speedo (Smiths makes one as well as speedhut.com. Speedhut allows you to customize the face of the gauge so you can get it reasonably close to the original Smiths). The electronic speedos can be driven by gps with an antenna, a hall effect counter, or I think you can get a counter that plugs into where the speedo cable goes in the tranny. I have the gps drive and I like it except that the first mile doesn't get registered in my odometer.
I think you will be able to use your 352 rear hoop but it may require some modification. Our own Andy Harwood did that modification. You may be able to find a picture of it but basically it looks like he flattend part of the tube to make room for the tranny.
Good luck!