Welcome Roger.
That's great you can build instruments! I wish I could!
You are right that the 620 and 420 are different. Quite different. While 400 series can have neck thru like the 600 series (some are set), the 600 series (excluding the 650) have a different profile.. meaning the neck sits higher off the body, allowing for the tiered pickguard you've likely seen, and the pickups sit on top of the body. 420's and 450's necks sit down low, hence the flat large pickguard, underneath which the pickups are sunk.
You may not realize it, but the design of Rick instruments is for the most part protected intellectual property. You may feel that your one-off built in the garage is a completely different animal than a Chinese factory making thousands of counterfeit guitars, and to most folks it is, but in the eyes of the law it isn't, so I'll just warn you that you will meet some resistance by posting your query here. Even if you never plan to sell it yourself - maybe leave it to your kids in your will, one day it could end up in the marketplace, and you'd be well advised to do something (like an internal marking) to prevent it from being confused with an original - that's a legal headache your heirs don't need. Just my $0.02, of course, not trying to rain on your first post here.
Have you considered building something original and unique that incorporates the functional aspects of the 420 that you like without infringing on the RIC trade dress? Best of luck!
