An SP1 Carbine has no forward assist either - other than the collapsible stock, different flash hider and handguards, its and SP1. I have one, no forward assist, metal collapsible stock, thin barrel. I've never even fired it - has been sitting in my safe since the early '90's.
These things used to go for upwards of $1,500. Really nice ones now sell for about $1,000. They do have and will continue to have some collector value - just not a whole lot right now with the flood of AR's in every conceivable shape and size. There are really only 3 things going for it: it's a Colt; it doesn't have a sear block so you can drop in a registered DIAS; and it has the right kind of bolt for a registered lightning link to work.
But, you don't need the SP1 as a host for your R-lightning Link or RDIAS - now there's tons of lowers, uppers, bolt configurations that can be made to work, I believe. So........it's a Colt.