Can't recommend anybody as I am not local. But checking over would really require a full strip down and rebuild, which is likely to not be needed.
The engine can have a basic check by yourself quite easily. First I would take all plugs out squirt some oil in each bore and leave for a day or two. You will need to bolt the starter motor up, and have a compression tester handy.
Spin the engine on the starter motor (beware, oil will probably splat out the plug holes, so a heavy cloth over the engine helps) Then in turn test teh compression for each cylinder, they should all be close in value.
Next, drain the oil out the sump, pop the sump off, and have a look at all the bearings. See if there are any that are bad, or the crank is scored up. If just some signs of wear, a ndew set of bearings can be fitted. Check for endfloat on the crank too, a smidge is OK, 2mm is not, but if the thrust bearings are still in place new ones usually take out all the wear.
That is really as far as you can go without a rebuild.
Gearbox, give the input shaft a waggle. If it really has a lot of play, it is an indicator that the mainshaft tip/bearings and/or front bearing are badly worn. Next, pop the top cover off and have a look. Rotate all the gears looking for broken teeth etc. Next step is a strip if you want to gio that far to inspect all the bearings and surfaces, but you are getting into serious cash again and it may not be needed.
The only real test of these components is to try them. If they are bad once fitted (do drive it before refitting all the interior etc, and you can run the engine sat in a tyre or a DIY frame if you are adverntorous) then have them rebuilt. Otherwise save the cash.